diff --git a/mysql-test/include/subselect_mat_cost.inc b/mysql-test/include/subselect_mat_cost.inc
new file mode 100644
index 00000000000..04b116e9527
--- /dev/null
+++ b/mysql-test/include/subselect_mat_cost.inc
@@ -0,0 +1,152 @@
+-- echo
+-- echo /* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+-- echo
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+-- echo
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+
+-- echo
+-- echo /*
+-- echo   B. "Natural" examples of subqueries without grouping that
+-- echo   cannot be flattened into semijoin.
+-- echo */
+
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+-- echo
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+-- echo UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+-- echo
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+-- echo
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+
+-- echo
+-- echo /* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+-- echo
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+-- echo
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+-- echo
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+-- echo
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+-- echo
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+
+-- echo
+-- echo /*
+-- echo   D. Subqueries for which materialization is not possible, and the
+-- echo   optimizer reverts to in-to-exists.
+-- echo */
+# The first two cases are rejected during the prepare phase by the procedure
+# subquery_types_allow_materialization().
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+-- echo
+# The following two subqueries return the result of a string function with a
+# blob argument, where the return type may be != blob. These are rejected during
+# cost-based optimization when attempting to create a temporary table.
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+-- echo
+
+
+-- echo
+-- echo /* E. Edge cases. */
+-- echo
+
+-- echo /* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+--error ER_ILLEGAL_SUBQUERY_OPTIMIZER_SWITCHES
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+set @@optimizer_switch = @save_optimizer_switch;
+
+-- echo /* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+
+-- echo /* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+-- echo UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+
+-- echo /* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+
+-- echo /* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+-- echo TODO this test produces wrong result due to missing logic to handle the case
+-- echo when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+select a1 from t1 where a1 in (select max(b1) from t2);
+-- echo
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+
+-- echo /* E.6 make_join_select detects impossible WHERE. *
+
+-- echo TODO
+
+-- echo /* E.7 constant optimization detects "no matching row in const table". */
+
+-- echo TODO
+
+-- echo /* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+
+-- echo
+-- echo /* F. UPDATE/DELETE with subqueries. */
+-- echo
+
+-- echo TODO
+-- echo
diff --git a/mysql-test/r/subselect3.result b/mysql-test/r/subselect3.result
index efb7a417bb0..5af3b5f9275 100644
--- a/mysql-test/r/subselect3.result
+++ b/mysql-test/r/subselect3.result
@@ -840,11 +840,16 @@ x	ROW(11, 12) = (SELECT MAX(x), 22)	ROW(11, 12) IN (SELECT MAX(x), 22)
 1	0	0
 2	0	0
 11	0	0
-# 2nd and 3rd columns should be same for x == 11 only
+# 2nd and 3rd columns should be same
+EXPLAIN SELECT a AS x, ROW(11, 12) = (SELECT MAX(x), 12), ROW(11, 12) IN (SELECT MAX(x), 12) FROM t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	
+3	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 SELECT a AS x, ROW(11, 12) = (SELECT MAX(x), 12), ROW(11, 12) IN (SELECT MAX(x), 12) FROM t1;
 x	ROW(11, 12) = (SELECT MAX(x), 12)	ROW(11, 12) IN (SELECT MAX(x), 12)
-1	0	1
-2	0	1
+1	0	0
+2	0	0
 11	1	1
 DROP TABLE t1;
 # both columns should be same
diff --git a/mysql-test/r/subselect3_jcl6.result b/mysql-test/r/subselect3_jcl6.result
index d24c1baa814..843e82d66b9 100644
--- a/mysql-test/r/subselect3_jcl6.result
+++ b/mysql-test/r/subselect3_jcl6.result
@@ -844,11 +844,16 @@ x	ROW(11, 12) = (SELECT MAX(x), 22)	ROW(11, 12) IN (SELECT MAX(x), 22)
 1	0	0
 2	0	0
 11	0	0
-# 2nd and 3rd columns should be same for x == 11 only
+# 2nd and 3rd columns should be same
+EXPLAIN SELECT a AS x, ROW(11, 12) = (SELECT MAX(x), 12), ROW(11, 12) IN (SELECT MAX(x), 12) FROM t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	
+3	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
 SELECT a AS x, ROW(11, 12) = (SELECT MAX(x), 12), ROW(11, 12) IN (SELECT MAX(x), 12) FROM t1;
 x	ROW(11, 12) = (SELECT MAX(x), 12)	ROW(11, 12) IN (SELECT MAX(x), 12)
-1	0	1
-2	0	1
+1	0	0
+2	0	0
 11	1	1
 DROP TABLE t1;
 # both columns should be same
diff --git a/mysql-test/r/subselect_mat.result b/mysql-test/r/subselect_mat.result
index 38cb13a26bc..30ed48d3563 100644
--- a/mysql-test/r/subselect_mat.result
+++ b/mysql-test/r/subselect_mat.result
@@ -30,7 +30,7 @@ create index it3i3 on t3i (c1, c2);
 insert into t1i select * from t1;
 insert into t2i select * from t2;
 insert into t3i select * from t3;
-set @@optimizer_switch='semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 /******************************************************************************
 * Simple tests.
 ******************************************************************************/
@@ -176,33 +176,33 @@ a1	a2
 1 - 02	2 - 02
 select * from t1 where (a1, a2) in (select b1, min(b2) from t2i limit 1,1);
 ERROR 42000: This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery'
-set @@optimizer_switch='default,semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=on';
 prepare st1 from
 "select * from t1 where (a1, a2) in (select b1, min(b2) from t2 where b1 > '0' group by b1)";
-set @@optimizer_switch='default,materialization=off';
+set @@optimizer_switch='materialization=off,in_to_exists=on,semijoin=on';
 execute st1;
 a1	a2
 1 - 01	2 - 01
 1 - 02	2 - 02
-set @@optimizer_switch='default,semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=on';
 execute st1;
 a1	a2
 1 - 01	2 - 01
 1 - 02	2 - 02
-set @@optimizer_switch='default,materialization=off';
+set @@optimizer_switch='materialization=off,in_to_exists=on,semijoin=on';
 prepare st1 from
 "select * from t1 where (a1, a2) in (select b1, min(b2) from t2 where b1 > '0' group by b1)";
-set @@optimizer_switch='default,semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 execute st1;
 a1	a2
 1 - 01	2 - 01
 1 - 02	2 - 02
-set @@optimizer_switch='default,materialization=off';
+set @@optimizer_switch='materialization=off,in_to_exists=on,semijoin=on';
 execute st1;
 a1	a2
 1 - 01	2 - 01
 1 - 02	2 - 02
-set @@optimizer_switch='default,semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 explain extended
 select * from t1 where (a1, a2) in (select b1, b2 from t2 order by b1, b2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
@@ -549,7 +549,7 @@ a1	a2
 Test that BLOBs are not materialized (except when arguments of some functions).
 */
 # force materialization to be always considered
-set @@optimizer_switch='semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 set @prefix_len = 6;
 set @blob_len = 16;
 set @suffix_len = @blob_len - @prefix_len;
@@ -951,7 +951,7 @@ insert into t1bit values (b'010', b'110');
 insert into t2bit values (b'001', b'101');
 insert into t2bit values (b'010', b'110');
 insert into t2bit values (b'110', b'111');
-set @@optimizer_switch='semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 explain extended select bin(a1), bin(a2)
 from t1bit
 where (a1, a2) in (select b1, b2 from t2bit);
@@ -994,7 +994,7 @@ drop table t1, t2, t3, t1i, t2i, t3i, columns;
 /******************************************************************************
 * Test the cache of the left operand of IN.
 ******************************************************************************/
-set @@optimizer_switch='semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 create table t1 (s1 int);
 create table t2 (s2 int);
 insert into t1 values (5),(1),(0);
@@ -1136,27 +1136,40 @@ drop table t2;
 create table t1 (a1 int key);
 create table t2 (b1 int);
 insert into t1 values (5);
+Only the last query returns correct result. Filed as BUG#40037.
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 explain select min(a1) from t1 where 7 in (select b1 from t2 group by b1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 2	SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
 select min(a1) from t1 where 7 in (select b1 from t2 group by b1);
 min(a1)
-set @@optimizer_switch='default,materialization=off';
+NULL
+set @@optimizer_switch='materialization=off,in_to_exists=on,semijoin=off';
 explain select min(a1) from t1 where 7 in (select b1 from t2 group by b1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 2	DEPENDENT SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
 select min(a1) from t1 where 7 in (select b1 from t2 group by b1);
 min(a1)
-set @@optimizer_switch='default,semijoin=off';
+NULL
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 explain select min(a1) from t1 where 7 in (select b1 from t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 2	SUBQUERY	t2	system	NULL	NULL	NULL	NULL	0	const row not found
 select min(a1) from t1 where 7 in (select b1 from t2);
 min(a1)
-set @@optimizer_switch='default,materialization=off';
+NULL
+set @@optimizer_switch='materialization=off,in_to_exists=on,semijoin=off';
+explain select min(a1) from t1 where 7 in (select b1 from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+select min(a1) from t1 where 7 in (select b1 from t2);
+min(a1)
+NULL
+set @@optimizer_switch='materialization=off,in_to_exists=off,semijoin=on';
 explain select min(a1) from t1 where 7 in (select b1 from t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
@@ -1167,7 +1180,7 @@ drop table t1,t2;
 create table t1 (a char(2), b varchar(10));
 insert into t1 values ('a',  'aaa');
 insert into t1 values ('aa', 'aaaa');
-set @@optimizer_switch='default,semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 explain select a,b from t1 where b in (select a from t1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
@@ -1187,7 +1200,7 @@ INSERT INTO t1 (f1, f2) VALUES (10, 1.668);
 CREATE TABLE t2 LIKE t1;
 INSERT INTO t2 VALUES (1, 1.789);
 INSERT INTO t2 VALUES (13, 1.454);
-SET @@optimizer_switch='default,semijoin=on,materialization=on';
+SET @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=on';
 EXPLAIN SELECT COUNT(*) FROM t1 WHERE (f1,f2) IN (SELECT f1,f2 FROM t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	subselect2	ALL	unique_key	NULL	NULL	NULL	2	
@@ -1208,7 +1221,7 @@ PRIMARY KEY (pk)
 INSERT INTO t1 VALUES (1,'o','ffff','ffff','ffoo'),(2,'f','ffff','ffff','ffff');
 CREATE TABLE t2 LIKE t1;
 INSERT INTO t2 VALUES (1,'i','iiii','iiii','iiii'),(2,'f','ffff','ffff','ffff');
-SET @@optimizer_switch='default,semijoin=on,materialization=on';
+SET @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=on';
 EXPLAIN SELECT pk FROM t1 WHERE (a) IN (SELECT a FROM t2 WHERE pk > 0);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	
@@ -1237,7 +1250,7 @@ i
 3
 4
 set @save_optimizer_switch=@@optimizer_switch;
-set session optimizer_switch='materialization=off';
+set session optimizer_switch='materialization=off,in_to_exists=on';
 select * from t1 where t1.i in (select t2.i from t2 join t3 where t2.i + t3.i = 5);
 i
 1
diff --git a/mysql-test/r/subselect_mat_cost.result b/mysql-test/r/subselect_mat_cost.result
new file mode 100644
index 00000000000..b5db804f7ff
--- /dev/null
+++ b/mysql-test/r/subselect_mat_cost.result
@@ -0,0 +1,3822 @@
+drop table if exists t1, t2, t1_1024, t2_1024;
+drop procedure if exists make_t1_indexes;
+drop procedure if exists make_t2_indexes;
+drop procedure if exists remove_t1_indexes;
+drop procedure if exists remove_t2_indexes;
+drop procedure if exists add_materialization_data;
+drop procedure if exists delete_materialization_data;
+drop procedure if exists set_all_columns_not_null;
+drop procedure if exists set_all_columns_nullable;
+create table t1 (a1 char(8), a2 char(8), a3 char(8), a4 int);
+insert into t1 values ('1 - 00', '2 - 00', '3 - 00', 0);
+insert into t1 values ('1 - 01', '2 - 01', '3 - 01', 1);
+insert into t1 values ('1 - 02', '2 - 02', '3 - 02', 2);
+create table t2 (b1 char(8), b2 char(8), b3 char(8), b4 int);
+insert into t2 values ('1 - 01', '2 - 01', '3 - 01', 1);
+insert into t2 values ('1 - 01', '2 - 01', '3 - 02', 2);
+insert into t2 values ('1 - 02', '2 - 02', '3 - 03', 3);
+insert into t2 values ('1 - 02', '2 - 02', '3 - 04', 4);
+insert into t2 values ('1 - 03', '2 - 03', '3 - 05', 5);
+create table t1_1024 (a1 blob(1024), a2 blob(1024));
+insert into t1_1024 values (concat('1 - 00', repeat('x', 1018)), concat('2 - 00', repeat('x', 1018)));
+insert into t1_1024 values (concat('1 - 01', repeat('x', 1018)), concat('2 - 01', repeat('x', 1018)));
+create table t2_1024 (b1 blob(1024), b2 blob(1024));
+insert into t2_1024 values (concat('1 - 01', repeat('x', 1018)), concat('2 - 01', repeat('x', 1018)));
+insert into t2_1024 values (concat('1 - 02', repeat('x', 1018)), concat('2 - 02', repeat('x', 1018)));
+insert into t2_1024 values (concat('1 - 03', repeat('x', 1018)), concat('2 - 03', repeat('x', 1018)));
+insert into t2_1024 values (concat('1 - 04', repeat('x', 1018)), concat('2 - 04', repeat('x', 1018)));
+create procedure make_t1_indexes()
+begin
+create index it1i1 on t1 (a1);
+create index it1i2 on t1 (a2);
+create index it1i3 on t1 (a1, a2);
+create index it1_1024i1 on t1_1024 (a1(6));
+create index it1_1024i2 on t1_1024 (a2(6));
+create index it1_1024i3 on t1_1024 (a1(6), a2(6));
+end|
+create procedure make_t2_indexes()
+begin
+create index it2i1 on t2 (b1);
+create index it2i2 on t2 (b2);
+create index it2i3 on t2 (b1, b2);
+create unique index it2i4 on t2 (b1, b2, b3);
+create index it2_1024i1 on t2_1024 (b1(6));
+create index it2_1024i2 on t2_1024 (b2(6));
+create index it2_1024i3 on t2_1024 (b1(6), b2(6));
+end|
+create procedure remove_t1_indexes()
+begin
+drop index it1i1 on t1;
+drop index it1i2 on t1;
+drop index it1i3 on t1;
+drop index it1_1024i1 on t1_1024;
+drop index it1_1024i2 on t1_1024;
+drop index it1_1024i3 on t1_1024;
+end|
+create procedure remove_t2_indexes()
+begin
+drop index it2i1 on t2;
+drop index it2i2 on t2;
+drop index it2i3 on t2;
+drop index it2i4 on t2;
+drop index it2_1024i1 on t2_1024;
+drop index it2_1024i2 on t2_1024;
+drop index it2_1024i3 on t2_1024;
+end|
+create procedure add_materialization_data()
+begin
+insert into t1 values ('1 - 03', '2 - 03', '3 - 03', 3);
+insert into t1 values ('1 - 04', '2 - 04', '3 - 04', 4);
+insert into t1 values ('1 - 05', '2 - 05', '3 - 05', 5);
+insert into t1 values ('1 - 06', '2 - 06', '3 - 06', 6);
+insert into t1 values ('1 - 07', '2 - 07', '3 - 07', 7);
+insert into t1_1024 values (concat('1 - 03', repeat('x', 1018)), concat('2 - 03', repeat('x', 1018)));
+end|
+create procedure delete_materialization_data()
+begin
+delete from t1 where a1 >= '1 - 03';
+delete from t1_1024 where a1 >= '1 - 03';
+end|
+create procedure set_all_columns_not_null()
+begin
+alter table t1 modify a1 char(8) not null, modify a2 char(8) not null, modify a3 char(8) not null;
+alter table t2 modify b1 char(8) not null, modify b2 char(8) not null, modify b3 char(8) not null;
+end|
+create procedure set_all_columns_nullable()
+begin
+alter table t1 modify a1 char(8) null, modify a2 char(8) null, modify a3 char(8) null;
+alter table t2 modify b1 char(8) null, modify b2 char(8) null, modify b3 char(8) null;
+end|
+
+/******************************************************************************
+1. Both materialization and in-to-exists are ON, make a cost-based choice.
+******************************************************************************/
+set @@optimizer_switch='materialization=on,in_to_exists=on';
+
+/* 1.1 In-to-exists is cheaper */
+call make_t1_indexes();
+/* 1.1.1 non-indexed table access */
+
+/* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using index
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+a1	a1 in (select b1 from t2 where b1 > '0')
+1 - 00	0
+1 - 01	1
+1 - 02	1
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	18	NULL	3	Using index
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	18	NULL	3	Using index
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+
+/*
+B. "Natural" examples of subqueries without grouping that
+cannot be flattened into semijoin.
+*/
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	18	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	18	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+a1	a2
+1 - 00	2 - 00
+1 - 01	2 - 01
+1 - 02	2 - 02
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i2	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+3	DEPENDENT UNION	t3	ALL	NULL	NULL	NULL	NULL	5	Using where
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+a2
+2 - 01
+2 - 02
+
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ref	it1i1,it1i3	it1i1	9	const	1	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+a1
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	18	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+a1	a2
+1 - 01	2 - 01
+1 - 02	2 - 02
+
+/* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using temporary; Using filesort
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+a1	a2	a3	a4
+
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+/*
+D. Subqueries for which materialization is not possible, and the
+optimizer reverts to in-to-exists.
+*/
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+
+
+/* E. Edge cases. */
+
+/* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+ERROR HY000: At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'.
+set @@optimizer_switch = @save_optimizer_switch;
+/* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+'1 - 03' in (select b1 from t2 where b1 > '0')
+1
+/* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i1,it1i2,it1i3	it1i3	18	NULL	3	Using where; Using index
+Warnings:
+Note	1249	Select 2 was reduced during optimization
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+a1
+1 - 02
+/* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	18	NULL	3	Using where; Using index
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+/* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+TODO this test produces wrong result due to missing logic to handle the case
+when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	
+select a1 from t1 where a1 in (select max(b1) from t2);
+a1
+
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+a1
+/* E.6 make_join_select detects impossible WHERE. *
+TODO
+/* E.7 constant optimization detects "no matching row in const table". */
+TODO
+/* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+'1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0')
+0
+
+/* F. UPDATE/DELETE with subqueries. */
+
+TODO
+
+/* 1.1.2 indexed table access, nullabale columns. */
+call make_t2_indexes();
+
+/* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using index
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i3	it2i1	9	func	2	Using index; Using where; Full scan on NULL key
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+a1	a1 in (select b1 from t2 where b1 > '0')
+1 - 00	0
+1 - 01	1
+1 - 02	1
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	18	NULL	3	Using index
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i2,it2i3	it2i3	9	func	2	Using index; Using where; Full scan on NULL key
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	18	NULL	3	Using index
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i2,it2i3	it2i3	9	func	2	Using index; Using where; Full scan on NULL key
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+
+/*
+B. "Natural" examples of subqueries without grouping that
+cannot be flattened into semijoin.
+*/
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	18	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i2	it2i2	9	func	2	Using index
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	18	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i2,it2i3	it2i4	18	func,func	1	Using index; Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+a1	a2
+1 - 00	2 - 00
+1 - 01	2 - 01
+1 - 02	2 - 02
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i2	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ref	it2i2	it2i2	9	func	2	Using index
+3	DEPENDENT UNION	t3	index	NULL	it2i4	27	NULL	5	Using where; Using index
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+a2
+2 - 01
+2 - 02
+
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ref	it1i1,it1i3	it1i1	9	const	1	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ref	it2i2	it2i2	9	const	1	Using index condition
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+a1
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	18	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i2,it2i3	it2i4	18	func,func	1	Using index; Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+a1	a2
+1 - 01	2 - 01
+1 - 02	2 - 02
+
+/* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i1	9	NULL	1	Using where; Using index
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	18	NULL	1	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	18	NULL	1	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	index	NULL	it2i4	27	NULL	1	Using index
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	index	NULL	it2i4	27	NULL	1	Using where; Using index
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+a1	a2	a3	a4
+
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	range	it2i4,it2i1,it2i3	it2i4	27	NULL	2	Using where; Using index for group-by
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+/*
+D. Subqueries for which materialization is not possible, and the
+optimizer reverts to in-to-exists.
+*/
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i3	it2_1024i3	9	func	1	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i2,it2_1024i3	it2_1024i1	9	func	2	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+
+
+/* E. Edge cases. */
+
+/* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+ERROR HY000: At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'.
+set @@optimizer_switch = @save_optimizer_switch;
+/* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i3	it2i1	9	const	2	Using index; Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+'1 - 03' in (select b1 from t2 where b1 > '0')
+1
+/* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i1,it1i2,it1i3	it1i3	18	NULL	3	Using where; Using index
+Warnings:
+Note	1249	Select 2 was reduced during optimization
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+a1
+1 - 02
+/* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	18	NULL	3	Using where; Using index
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+/* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+TODO this test produces wrong result due to missing logic to handle the case
+when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+select a1 from t1 where a1 in (select max(b1) from t2);
+a1
+
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No matching min/max row
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+a1
+/* E.6 make_join_select detects impossible WHERE. *
+TODO
+/* E.7 constant optimization detects "no matching row in const table". */
+TODO
+/* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+'1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0')
+0
+
+/* F. UPDATE/DELETE with subqueries. */
+
+TODO
+
+/* 1.1.3 indexed table access, non-nullabale columns. */
+call set_all_columns_not_null();
+
+/* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	8	NULL	3	Using index
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i3	it2i4	8	func	1	Using index; Using where
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+a1	a1 in (select b1 from t2 where b1 > '0')
+1 - 00	0
+1 - 01	1
+1 - 02	1
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	16	NULL	3	Using index
+2	DEPENDENT SUBQUERY	t2	ref	it2i4,it2i1,it2i2,it2i3	it2i4	8	func	2	Using where; Using index
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	16	NULL	3	Using index
+2	DEPENDENT SUBQUERY	t2	ref	it2i4,it2i1,it2i2,it2i3	it2i4	8	func	2	Using where; Using index
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+
+/*
+B. "Natural" examples of subqueries without grouping that
+cannot be flattened into semijoin.
+*/
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	16	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i2	it2i2	8	func	2	Using index
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	16	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i2,it2i3	it2i4	16	func,func	1	Using index; Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+a1	a2
+1 - 00	2 - 00
+1 - 01	2 - 01
+1 - 02	2 - 02
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i2	8	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ref	it2i2	it2i2	8	func	2	Using index
+3	DEPENDENT UNION	t3	index	NULL	it2i4	24	NULL	5	Using where; Using index
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+a2
+2 - 01
+2 - 02
+
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ref	it1i1,it1i3	it1i1	8	const	1	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ref	it2i2	it2i2	8	const	1	Using index condition
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+a1
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	16	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i2,it2i3	it2i4	16	func,func	1	Using index; Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+a1	a2
+1 - 01	2 - 01
+1 - 02	2 - 02
+
+/* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i1	8	NULL	1	Using where; Using index
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	16	NULL	1	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	16	NULL	1	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	index	NULL	it2i4	24	NULL	1	Using index
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	index	NULL	it2i4	24	NULL	1	Using where; Using index
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+a1	a2	a3	a4
+
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2	range	it2i4,it2i1,it2i3	it2i4	24	NULL	2	Using where; Using index for group-by
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+/*
+D. Subqueries for which materialization is not possible, and the
+optimizer reverts to in-to-exists.
+*/
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i3	it2_1024i3	9	func	1	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i2,it2_1024i3	it2_1024i1	9	func	2	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+
+
+/* E. Edge cases. */
+
+/* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+ERROR HY000: At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'.
+set @@optimizer_switch = @save_optimizer_switch;
+/* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i3	it2i1	8	const	5	Using index; Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+'1 - 03' in (select b1 from t2 where b1 > '0')
+1
+/* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i1,it1i2,it1i3	it1i3	16	NULL	3	Using where; Using index
+Warnings:
+Note	1249	Select 2 was reduced during optimization
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	8	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+a1
+1 - 02
+/* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	16	NULL	3	Using where; Using index
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+/* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+TODO this test produces wrong result due to missing logic to handle the case
+when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	8	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+select a1 from t1 where a1 in (select max(b1) from t2);
+a1
+
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	8	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No matching min/max row
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+a1
+/* E.6 make_join_select detects impossible WHERE. *
+TODO
+/* E.7 constant optimization detects "no matching row in const table". */
+TODO
+/* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+'1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0')
+0
+
+/* F. UPDATE/DELETE with subqueries. */
+
+TODO
+
+call set_all_columns_nullable();
+
+/* 1.2 Materialization is cheaper */
+call add_materialization_data();
+call remove_t1_indexes();
+/* 1.2.1 non-indexed table access */
+call remove_t2_indexes();
+
+/* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+a1	a1 in (select b1 from t2 where b1 > '0')
+1 - 00	0
+1 - 01	1
+1 - 02	1
+1 - 03	1
+1 - 04	0
+1 - 05	0
+1 - 06	0
+1 - 07	0
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+1 - 03	2 - 03	1
+1 - 04	2 - 04	0
+1 - 05	2 - 05	0
+1 - 06	2 - 06	0
+1 - 07	2 - 07	0
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+1 - 03	2 - 03	1
+1 - 04	2 - 04	0
+1 - 05	2 - 05	0
+1 - 06	2 - 06	0
+1 - 07	2 - 07	0
+
+/*
+B. "Natural" examples of subqueries without grouping that
+cannot be flattened into semijoin.
+*/
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+a1	a2
+1 - 00	2 - 00
+1 - 01	2 - 01
+1 - 02	2 - 02
+1 - 03	2 - 03
+1 - 04	2 - 04
+1 - 05	2 - 05
+1 - 06	2 - 06
+1 - 07	2 - 07
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+3	DEPENDENT UNION	t3	ALL	NULL	NULL	NULL	NULL	5	Using where
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+a2
+2 - 01
+2 - 02
+2 - 03
+
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+a1
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+a1	a2
+1 - 01	2 - 01
+1 - 02	2 - 02
+1 - 03	2 - 03
+
+/* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using temporary; Using filesort
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+a1	a2	a3	a4
+
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+/*
+D. Subqueries for which materialization is not possible, and the
+optimizer reverts to in-to-exists.
+*/
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+
+
+/* E. Edge cases. */
+
+/* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+ERROR HY000: At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'.
+set @@optimizer_switch = @save_optimizer_switch;
+/* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+'1 - 03' in (select b1 from t2 where b1 > '0')
+1
+/* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+Warnings:
+Note	1249	Select 2 was reduced during optimization
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+a1
+1 - 02
+1 - 03
+/* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+/* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+TODO this test produces wrong result due to missing logic to handle the case
+when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	
+select a1 from t1 where a1 in (select max(b1) from t2);
+a1
+1 - 03
+
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+a1
+/* E.6 make_join_select detects impossible WHERE. *
+TODO
+/* E.7 constant optimization detects "no matching row in const table". */
+TODO
+/* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+'1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0')
+0
+
+/* F. UPDATE/DELETE with subqueries. */
+
+TODO
+
+/* 1.2.2 indexed table access, nullabale columns. */
+call make_t2_indexes();
+
+/* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i1	9	NULL	5	Using where; Using index
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+a1	a1 in (select b1 from t2 where b1 > '0')
+1 - 00	0
+1 - 01	1
+1 - 02	1
+1 - 03	1
+1 - 04	0
+1 - 05	0
+1 - 06	0
+1 - 07	0
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i2,it2i3	it2i3	18	NULL	5	Using where; Using index
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+1 - 03	2 - 03	1
+1 - 04	2 - 04	0
+1 - 05	2 - 05	0
+1 - 06	2 - 06	0
+1 - 07	2 - 07	0
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	SUBQUERY	t2	range	it2i4,it2i1,it2i2,it2i3	it2i3	9	NULL	4	Using where; Using index
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+1 - 03	2 - 03	1
+1 - 04	2 - 04	0
+1 - 05	2 - 05	0
+1 - 06	2 - 06	0
+1 - 07	2 - 07	0
+
+/*
+B. "Natural" examples of subqueries without grouping that
+cannot be flattened into semijoin.
+*/
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	index	it2i2	it2i2	9	NULL	5	Using index
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i2,it2i3	it2i3	18	NULL	5	Using where; Using index
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+a1	a2
+1 - 00	2 - 00
+1 - 01	2 - 01
+1 - 02	2 - 02
+1 - 03	2 - 03
+1 - 04	2 - 04
+1 - 05	2 - 05
+1 - 06	2 - 06
+1 - 07	2 - 07
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ref	it2i2	it2i2	9	func	2	Using index
+3	DEPENDENT UNION	t3	index	NULL	it2i4	27	NULL	5	Using where; Using index
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+a2
+2 - 01
+2 - 02
+2 - 03
+
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ref	it2i2	it2i2	9	const	1	Using index condition
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+a1
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i2,it2i3	it2i4	27	NULL	5	Using index
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+a1	a2
+1 - 01	2 - 01
+1 - 02	2 - 02
+1 - 03	2 - 03
+
+/* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i1	9	NULL	5	Using where; Using index
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	18	NULL	5	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	18	NULL	5	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	range	NULL	it2i4	27	NULL	6	Using index for group-by
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	range	NULL	it2i4	27	NULL	6	Using where; Using index for group-by
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+a1	a2	a3	a4
+
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	range	it2i4,it2i1,it2i3	it2i4	27	NULL	2	Using where; Using index for group-by
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+/*
+D. Subqueries for which materialization is not possible, and the
+optimizer reverts to in-to-exists.
+*/
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i3	it2_1024i3	9	func	1	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i2,it2_1024i3	it2_1024i1	9	func	2	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+
+
+/* E. Edge cases. */
+
+/* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+ERROR HY000: At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'.
+set @@optimizer_switch = @save_optimizer_switch;
+/* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i3	it2i1	9	const	2	Using index; Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+'1 - 03' in (select b1 from t2 where b1 > '0')
+1
+/* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+Warnings:
+Note	1249	Select 2 was reduced during optimization
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+a1
+1 - 02
+1 - 03
+/* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+/* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+TODO this test produces wrong result due to missing logic to handle the case
+when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+select a1 from t1 where a1 in (select max(b1) from t2);
+a1
+1 - 03
+
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No matching min/max row
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+a1
+/* E.6 make_join_select detects impossible WHERE. *
+TODO
+/* E.7 constant optimization detects "no matching row in const table". */
+TODO
+/* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+'1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0')
+0
+
+/* F. UPDATE/DELETE with subqueries. */
+
+TODO
+
+/* 1.2.3 indexed table access, non-nullabale columns. */
+call set_all_columns_not_null();
+
+/* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i1	8	NULL	5	Using where; Using index
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+a1	a1 in (select b1 from t2 where b1 > '0')
+1 - 00	0
+1 - 01	1
+1 - 02	1
+1 - 03	1
+1 - 04	0
+1 - 05	0
+1 - 06	0
+1 - 07	0
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i2,it2i3	it2i3	16	NULL	5	Using where; Using index
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+1 - 03	2 - 03	1
+1 - 04	2 - 04	0
+1 - 05	2 - 05	0
+1 - 06	2 - 06	0
+1 - 07	2 - 07	0
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	SUBQUERY	t2	range	it2i4,it2i1,it2i2,it2i3	it2i3	8	NULL	4	Using where; Using index
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+1 - 03	2 - 03	1
+1 - 04	2 - 04	0
+1 - 05	2 - 05	0
+1 - 06	2 - 06	0
+1 - 07	2 - 07	0
+
+/*
+B. "Natural" examples of subqueries without grouping that
+cannot be flattened into semijoin.
+*/
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	index	it2i2	it2i2	8	NULL	5	Using index
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i2,it2i3	it2i3	16	NULL	5	Using where; Using index
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+a1	a2
+1 - 00	2 - 00
+1 - 01	2 - 01
+1 - 02	2 - 02
+1 - 03	2 - 03
+1 - 04	2 - 04
+1 - 05	2 - 05
+1 - 06	2 - 06
+1 - 07	2 - 07
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ref	it2i2	it2i2	8	func	2	Using index
+3	DEPENDENT UNION	t3	index	NULL	it2i4	24	NULL	5	Using where; Using index
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+a2
+2 - 01
+2 - 02
+2 - 03
+
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	ref	it2i2	it2i2	8	const	1	Using index condition
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+a1
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i2,it2i3	it2i4	24	NULL	5	Using index
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+a1	a2
+1 - 01	2 - 01
+1 - 02	2 - 02
+1 - 03	2 - 03
+
+/* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i1	8	NULL	5	Using where; Using index
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	16	NULL	5	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	16	NULL	5	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	range	NULL	it2i4	24	NULL	6	Using index for group-by
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	range	NULL	it2i4	24	NULL	6	Using where; Using index for group-by
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+a1	a2	a3	a4
+
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	t2	range	it2i4,it2i1,it2i3	it2i4	24	NULL	2	Using where; Using index for group-by
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+/*
+D. Subqueries for which materialization is not possible, and the
+optimizer reverts to in-to-exists.
+*/
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i3	it2_1024i3	9	func	1	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i2,it2_1024i3	it2_1024i1	9	func	2	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+
+
+/* E. Edge cases. */
+
+/* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+ERROR HY000: At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'.
+set @@optimizer_switch = @save_optimizer_switch;
+/* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i3	it2i1	8	const	5	Using index; Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+'1 - 03' in (select b1 from t2 where b1 > '0')
+1
+/* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+Warnings:
+Note	1249	Select 2 was reduced during optimization
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+a1
+1 - 02
+1 - 03
+/* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+/* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+TODO this test produces wrong result due to missing logic to handle the case
+when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+select a1 from t1 where a1 in (select max(b1) from t2);
+a1
+1 - 03
+
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No matching min/max row
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+a1
+/* E.6 make_join_select detects impossible WHERE. *
+TODO
+/* E.7 constant optimization detects "no matching row in const table". */
+TODO
+/* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+'1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0')
+0
+
+/* F. UPDATE/DELETE with subqueries. */
+
+TODO
+
+call set_all_columns_nullable();
+/******************************************************************************
+2. Materialization is OFF, in-to-exists is ON, materialization is cheaper.
+******************************************************************************/
+set @@optimizer_switch='materialization=off,in_to_exists=on';
+/* 2.1 non-indexed table access */
+call remove_t2_indexes();
+
+/* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+a1	a1 in (select b1 from t2 where b1 > '0')
+1 - 00	0
+1 - 01	1
+1 - 02	1
+1 - 03	1
+1 - 04	0
+1 - 05	0
+1 - 06	0
+1 - 07	0
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+1 - 03	2 - 03	1
+1 - 04	2 - 04	0
+1 - 05	2 - 05	0
+1 - 06	2 - 06	0
+1 - 07	2 - 07	0
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+1 - 03	2 - 03	1
+1 - 04	2 - 04	0
+1 - 05	2 - 05	0
+1 - 06	2 - 06	0
+1 - 07	2 - 07	0
+
+/*
+B. "Natural" examples of subqueries without grouping that
+cannot be flattened into semijoin.
+*/
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+a1	a2
+1 - 00	2 - 00
+1 - 01	2 - 01
+1 - 02	2 - 02
+1 - 03	2 - 03
+1 - 04	2 - 04
+1 - 05	2 - 05
+1 - 06	2 - 06
+1 - 07	2 - 07
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+3	DEPENDENT UNION	t3	ALL	NULL	NULL	NULL	NULL	5	Using where
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+a2
+2 - 01
+2 - 02
+2 - 03
+
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+a1
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+a1	a2
+1 - 01	2 - 01
+1 - 02	2 - 02
+1 - 03	2 - 03
+
+/* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using temporary; Using filesort
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+a1	a2	a3	a4
+
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+/*
+D. Subqueries for which materialization is not possible, and the
+optimizer reverts to in-to-exists.
+*/
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+
+
+/* E. Edge cases. */
+
+/* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+ERROR HY000: At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'.
+set @@optimizer_switch = @save_optimizer_switch;
+/* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+'1 - 03' in (select b1 from t2 where b1 > '0')
+1
+/* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+Warnings:
+Note	1249	Select 2 was reduced during optimization
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+a1
+1 - 02
+1 - 03
+/* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+/* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+TODO this test produces wrong result due to missing logic to handle the case
+when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	
+select a1 from t1 where a1 in (select max(b1) from t2);
+a1
+1 - 03
+
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+a1
+/* E.6 make_join_select detects impossible WHERE. *
+TODO
+/* E.7 constant optimization detects "no matching row in const table". */
+TODO
+/* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+'1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0')
+0
+
+/* F. UPDATE/DELETE with subqueries. */
+
+TODO
+
+/* 2.2 indexed table access, nullabale columns. */
+call make_t2_indexes();
+
+/* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i3	it2i1	9	func	2	Using index; Using where; Full scan on NULL key
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+a1	a1 in (select b1 from t2 where b1 > '0')
+1 - 00	0
+1 - 01	1
+1 - 02	1
+1 - 03	1
+1 - 04	0
+1 - 05	0
+1 - 06	0
+1 - 07	0
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i2,it2i3	it2i3	9	func	2	Using index; Using where; Full scan on NULL key
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+1 - 03	2 - 03	1
+1 - 04	2 - 04	0
+1 - 05	2 - 05	0
+1 - 06	2 - 06	0
+1 - 07	2 - 07	0
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i2,it2i3	it2i3	9	func	2	Using index; Using where; Full scan on NULL key
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+1 - 03	2 - 03	1
+1 - 04	2 - 04	0
+1 - 05	2 - 05	0
+1 - 06	2 - 06	0
+1 - 07	2 - 07	0
+
+/*
+B. "Natural" examples of subqueries without grouping that
+cannot be flattened into semijoin.
+*/
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i2	it2i2	9	func	2	Using index
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i2,it2i3	it2i4	18	func,func	1	Using index; Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+a1	a2
+1 - 00	2 - 00
+1 - 01	2 - 01
+1 - 02	2 - 02
+1 - 03	2 - 03
+1 - 04	2 - 04
+1 - 05	2 - 05
+1 - 06	2 - 06
+1 - 07	2 - 07
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ref	it2i2	it2i2	9	func	2	Using index
+3	DEPENDENT UNION	t3	index	NULL	it2i4	27	NULL	5	Using where; Using index
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+a2
+2 - 01
+2 - 02
+2 - 03
+
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ref	it2i2	it2i2	9	const	1	Using index condition
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+a1
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i2,it2i3	it2i4	18	func,func	1	Using index; Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+a1	a2
+1 - 01	2 - 01
+1 - 02	2 - 02
+1 - 03	2 - 03
+
+/* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i1	9	NULL	1	Using where; Using index
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	18	NULL	1	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	18	NULL	1	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index	NULL	it2i4	27	NULL	1	Using index
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index	NULL	it2i4	27	NULL	1	Using where; Using index
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+a1	a2	a3	a4
+
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	range	it2i4,it2i1,it2i3	it2i4	27	NULL	2	Using where; Using index for group-by
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+/*
+D. Subqueries for which materialization is not possible, and the
+optimizer reverts to in-to-exists.
+*/
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i3	it2_1024i3	9	func	1	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i2,it2_1024i3	it2_1024i1	9	func	2	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+
+
+/* E. Edge cases. */
+
+/* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+ERROR HY000: At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'.
+set @@optimizer_switch = @save_optimizer_switch;
+/* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i3	it2i1	9	const	2	Using index; Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+'1 - 03' in (select b1 from t2 where b1 > '0')
+1
+/* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+Warnings:
+Note	1249	Select 2 was reduced during optimization
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+a1
+1 - 02
+1 - 03
+/* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+/* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+TODO this test produces wrong result due to missing logic to handle the case
+when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+select a1 from t1 where a1 in (select max(b1) from t2);
+a1
+1 - 03
+
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No matching min/max row
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+a1
+/* E.6 make_join_select detects impossible WHERE. *
+TODO
+/* E.7 constant optimization detects "no matching row in const table". */
+TODO
+/* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+'1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0')
+0
+
+/* F. UPDATE/DELETE with subqueries. */
+
+TODO
+
+/* 2.3 indexed table access, non-nullabale columns. */
+call set_all_columns_not_null();
+
+/* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i3	it2i4	8	func	1	Using index; Using where
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+a1	a1 in (select b1 from t2 where b1 > '0')
+1 - 00	0
+1 - 01	1
+1 - 02	1
+1 - 03	1
+1 - 04	0
+1 - 05	0
+1 - 06	0
+1 - 07	0
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	DEPENDENT SUBQUERY	t2	ref	it2i4,it2i1,it2i2,it2i3	it2i4	8	func	2	Using where; Using index
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+1 - 03	2 - 03	1
+1 - 04	2 - 04	0
+1 - 05	2 - 05	0
+1 - 06	2 - 06	0
+1 - 07	2 - 07	0
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	
+2	DEPENDENT SUBQUERY	t2	ref	it2i4,it2i1,it2i2,it2i3	it2i4	8	func	2	Using where; Using index
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+1 - 03	2 - 03	1
+1 - 04	2 - 04	0
+1 - 05	2 - 05	0
+1 - 06	2 - 06	0
+1 - 07	2 - 07	0
+
+/*
+B. "Natural" examples of subqueries without grouping that
+cannot be flattened into semijoin.
+*/
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i2	it2i2	8	func	2	Using index
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i2,it2i3	it2i4	16	func,func	1	Using index; Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+a1	a2
+1 - 00	2 - 00
+1 - 01	2 - 01
+1 - 02	2 - 02
+1 - 03	2 - 03
+1 - 04	2 - 04
+1 - 05	2 - 05
+1 - 06	2 - 06
+1 - 07	2 - 07
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ref	it2i2	it2i2	8	func	2	Using index
+3	DEPENDENT UNION	t3	index	NULL	it2i4	24	NULL	5	Using where; Using index
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+a2
+2 - 01
+2 - 02
+2 - 03
+
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	ref	it2i2	it2i2	8	const	1	Using index condition
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+a1
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i2,it2i3	it2i4	16	func,func	1	Using index; Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+a1	a2
+1 - 01	2 - 01
+1 - 02	2 - 02
+1 - 03	2 - 03
+
+/* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i1	8	NULL	1	Using where; Using index
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	16	NULL	1	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	16	NULL	1	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+1 - 03	2 - 03	3 - 03	3
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index	NULL	it2i4	24	NULL	1	Using index
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	index	NULL	it2i4	24	NULL	1	Using where; Using index
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+a1	a2	a3	a4
+
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	t2	range	it2i4,it2i1,it2i3	it2i4	24	NULL	2	Using where; Using index for group-by
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+/*
+D. Subqueries for which materialization is not possible, and the
+optimizer reverts to in-to-exists.
+*/
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i3	it2_1024i3	9	func	1	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i2,it2_1024i3	it2_1024i1	9	func	2	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+1 - 03x	2 - 03x
+
+
+/* E. Edge cases. */
+
+/* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+ERROR HY000: At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'.
+set @@optimizer_switch = @save_optimizer_switch;
+/* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i3	it2i1	8	const	5	Using index; Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+'1 - 03' in (select b1 from t2 where b1 > '0')
+1
+/* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+Warnings:
+Note	1249	Select 2 was reduced during optimization
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+a1
+1 - 02
+1 - 03
+/* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+1 - 03
+1 - 04
+1 - 05
+1 - 06
+1 - 07
+/* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+TODO this test produces wrong result due to missing logic to handle the case
+when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+select a1 from t1 where a1 in (select max(b1) from t2);
+a1
+1 - 03
+
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	8	Using where
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No matching min/max row
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+a1
+/* E.6 make_join_select detects impossible WHERE. *
+TODO
+/* E.7 constant optimization detects "no matching row in const table". */
+TODO
+/* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+'1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0')
+0
+
+/* F. UPDATE/DELETE with subqueries. */
+
+TODO
+
+call set_all_columns_nullable();
+/******************************************************************************
+3. Materialization is ON, in-to-exists is OFF, in-to-exists is cheaper.
+******************************************************************************/
+set @@optimizer_switch='materialization=on,in_to_exists=off';
+call delete_materialization_data();
+call make_t1_indexes();
+/* 3.1 non-indexed table access */
+call remove_t2_indexes();
+
+/* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using index
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+a1	a1 in (select b1 from t2 where b1 > '0')
+1 - 00	0
+1 - 01	1
+1 - 02	1
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	18	NULL	3	Using index
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	18	NULL	3	Using index
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+
+/*
+B. "Natural" examples of subqueries without grouping that
+cannot be flattened into semijoin.
+*/
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	18	NULL	3	Using where; Using index
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	18	NULL	3	Using where; Using index
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+a1	a2
+1 - 00	2 - 00
+1 - 01	2 - 01
+1 - 02	2 - 02
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i2	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+3	DEPENDENT UNION	t3	ALL	NULL	NULL	NULL	NULL	5	Using where
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+a2
+2 - 01
+2 - 02
+
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ref	it1i1,it1i3	it1i1	9	const	1	Using where; Using index
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+a1
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	18	NULL	3	Using where; Using index
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+a1	a2
+1 - 01	2 - 01
+1 - 02	2 - 02
+
+/* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using temporary; Using filesort
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+a1	a2	a3	a4
+
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where; Using temporary; Using filesort
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+/*
+D. Subqueries for which materialization is not possible, and the
+optimizer reverts to in-to-exists.
+*/
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	ALL	NULL	NULL	NULL	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+
+
+/* E. Edge cases. */
+
+/* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+ERROR HY000: At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'.
+set @@optimizer_switch = @save_optimizer_switch;
+/* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+'1 - 03' in (select b1 from t2 where b1 > '0')
+1
+/* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i1,it1i2,it1i3	it1i3	18	NULL	3	Using where; Using index
+Warnings:
+Note	1249	Select 2 was reduced during optimization
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+a1
+1 - 02
+/* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	18	NULL	3	Using where; Using index
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+/* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+TODO this test produces wrong result due to missing logic to handle the case
+when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using where; Using index
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	
+select a1 from t1 where a1 in (select max(b1) from t2);
+a1
+
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using where; Using index
+2	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+a1
+/* E.6 make_join_select detects impossible WHERE. *
+TODO
+/* E.7 constant optimization detects "no matching row in const table". */
+TODO
+/* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	5	Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+'1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0')
+0
+
+/* F. UPDATE/DELETE with subqueries. */
+
+TODO
+
+/* 3.2 indexed table access, nullabale columns. */
+call make_t2_indexes();
+
+/* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using index
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i1	9	NULL	5	Using where; Using index
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+a1	a1 in (select b1 from t2 where b1 > '0')
+1 - 00	0
+1 - 01	1
+1 - 02	1
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	18	NULL	3	Using index
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	18	NULL	5	Using where; Using index
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	18	NULL	3	Using index
+2	SUBQUERY	t2	range	it2i4,it2i1,it2i3	it2i3	9	NULL	4	Using where; Using index
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+
+/*
+B. "Natural" examples of subqueries without grouping that
+cannot be flattened into semijoin.
+*/
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	18	NULL	3	Using where; Using index
+2	SUBQUERY	t2	index	NULL	it2i2	9	NULL	5	Using index
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	18	NULL	3	Using where; Using index
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	18	NULL	5	Using where; Using index
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+a1	a2
+1 - 00	2 - 00
+1 - 01	2 - 01
+1 - 02	2 - 02
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i2	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ref	it2i2	it2i2	9	func	2	Using index
+3	DEPENDENT UNION	t3	index	NULL	it2i4	27	NULL	5	Using where; Using index
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+a2
+2 - 01
+2 - 02
+
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ref	it1i1,it1i3	it1i1	9	const	1	Using where; Using index
+2	SUBQUERY	t2	ref	it2i2	it2i2	9	const	1	Using index condition
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+a1
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	18	NULL	3	Using where; Using index
+2	SUBQUERY	t2	index	NULL	it2i4	27	NULL	5	Using index
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+a1	a2
+1 - 01	2 - 01
+1 - 02	2 - 02
+
+/* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i1	9	NULL	5	Using where; Using index
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	18	NULL	5	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	18	NULL	5	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	range	NULL	it2i4	27	NULL	6	Using index for group-by
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	range	NULL	it2i4	27	NULL	6	Using where; Using index for group-by
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+a1	a2	a3	a4
+
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	range	it2i4,it2i1,it2i3	it2i4	27	NULL	2	Using where; Using index for group-by
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+/*
+D. Subqueries for which materialization is not possible, and the
+optimizer reverts to in-to-exists.
+*/
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i3	it2_1024i3	9	func	1	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i2,it2_1024i3	it2_1024i1	9	func	2	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+
+
+/* E. Edge cases. */
+
+/* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+ERROR HY000: At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'.
+set @@optimizer_switch = @save_optimizer_switch;
+/* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i3	it2i1	9	const	2	Using index; Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+'1 - 03' in (select b1 from t2 where b1 > '0')
+1
+/* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i1,it1i2,it1i3	it1i3	18	NULL	3	Using where; Using index
+Warnings:
+Note	1249	Select 2 was reduced during optimization
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+a1
+1 - 02
+/* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	18	NULL	3	Using where; Using index
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+/* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+TODO this test produces wrong result due to missing logic to handle the case
+when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+select a1 from t1 where a1 in (select max(b1) from t2);
+a1
+
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	9	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No matching min/max row
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+a1
+/* E.6 make_join_select detects impossible WHERE. *
+TODO
+/* E.7 constant optimization detects "no matching row in const table". */
+TODO
+/* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+'1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0')
+0
+
+/* F. UPDATE/DELETE with subqueries. */
+
+TODO
+
+/* 3.3 indexed table access, non-nullabale columns. */
+call set_all_columns_not_null();
+
+/* A. Subqueries in the SELECT clause. */
+explain
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	8	NULL	3	Using index
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i1	8	NULL	5	Using where; Using index
+select a1, a1 in (select b1 from t2 where b1 > '0') from t1;
+a1	a1 in (select b1 from t2 where b1 > '0')
+1 - 00	0
+1 - 01	1
+1 - 02	1
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	16	NULL	3	Using index
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	16	NULL	5	Using where; Using index
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+
+explain
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	16	NULL	3	Using index
+2	SUBQUERY	t2	range	it2i4,it2i1,it2i3	it2i3	8	NULL	4	Using where; Using index
+select a1, a2, (a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9') from t1;
+a1	a2	(a1, a2) in (select b1, b2 from t2 where b1 > '0' and b1 < '9')
+1 - 00	2 - 00	0
+1 - 01	2 - 01	1
+1 - 02	2 - 02	1
+
+/*
+B. "Natural" examples of subqueries without grouping that
+cannot be flattened into semijoin.
+*/
+explain
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	16	NULL	3	Using where; Using index
+2	SUBQUERY	t2	index	NULL	it2i2	8	NULL	5	Using index
+select a1 from t1 where a1 in (select b2 from t2) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	16	NULL	3	Using where; Using index
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	16	NULL	5	Using where; Using index
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0') or a2 < '9';
+a1	a2
+1 - 00	2 - 00
+1 - 01	2 - 01
+1 - 02	2 - 02
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i2	8	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	t2	ref	it2i2	it2i2	8	func	2	Using index
+3	DEPENDENT UNION	t3	index	NULL	it2i4	24	NULL	5	Using where; Using index
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a2 from t1 where a2 in (select b2 from t2 UNION select b3 from t2 as t3);
+a2
+2 - 01
+2 - 02
+
+explain
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ref	it1i1,it1i3	it1i1	8	const	1	Using where; Using index
+2	SUBQUERY	t2	ref	it2i2	it2i2	8	const	1	Using index condition
+select a1 from t1 where a1 = '1 - 02' and a1 in (select max(b1) from t2 where b2 = '2 - 02');
+a1
+1 - 02
+
+explain
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i3	16	NULL	3	Using where; Using index
+2	SUBQUERY	t2	index	NULL	it2i4	24	NULL	5	Using index
+select a1, a2 from t1 where (a1, a2) in (select b1, b2 from t2 order by b3);
+a1	a2
+1 - 01	2 - 01
+1 - 02	2 - 02
+
+/* C. Subqueries in the WHERE clause with GROUP BY. */
+explain
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i1	8	NULL	5	Using where; Using index
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	16	NULL	5	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	index	it2i4,it2i1,it2i3	it2i3	16	NULL	5	Using where; Using index
+select * from t1 where (a1, a2) in (select b1, b2 from t2 where b1 > '0' group by b1, b2 having b2 <  '2 - 04');
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+1 - 02	2 - 02	3 - 02	2
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	range	NULL	it2i4	24	NULL	6	Using index for group-by
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 group by b1, b2, b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+explain
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	range	NULL	it2i4	24	NULL	6	Using where; Using index for group-by
+select * from t1 where (a1, a2, a3) in (select b1, b2, b3 from t2 where b3 = '3 - 02' group by b1, b2);
+a1	a2	a3	a4
+
+explain
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
+2	SUBQUERY	t2	range	it2i4,it2i1,it2i3	it2i4	24	NULL	2	Using where; Using index for group-by
+select * from t1 where (a1,a2,a3) in (select b1,b2,b3 from t2 where b1 = '1 - 01' group by b1,b2,b3);
+a1	a2	a3	a4
+1 - 01	2 - 01	3 - 01	1
+
+/*
+D. Subqueries for which materialization is not possible, and the
+optimizer reverts to in-to-exists.
+*/
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i3	it2_1024i3	9	func	1	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select b1 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	index_subquery	it2_1024i1,it2_1024i2,it2_1024i3	it2_1024i1	9	func	2	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select b1, b2 from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+
+explain
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where a1 in (select substring(b1,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+explain
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1_1024	ALL	it1_1024i2	NULL	NULL	NULL	2	Using where
+2	DEPENDENT SUBQUERY	t2_1024	range	it2_1024i1,it2_1024i3	it2_1024i1	9	NULL	4	Using where
+select left(a1,7), left(a2,7) from t1_1024 where (a1,a2) in (select substring(b1,1,1024), substring(b2,1,1024) from t2_1024 where b1 > '0') or a2 < '9';
+left(a1,7)	left(a2,7)
+1 - 00x	2 - 00x
+1 - 01x	2 - 01x
+
+
+/* E. Edge cases. */
+
+/* E.1 Both materialization and in_to_exists cannot be off. */
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch = 'materialization=off,in_to_exists=off';
+select * from t1 where a1 in (select b1 from t2 where b1 > '0' group by b1);
+ERROR HY000: At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'.
+set @@optimizer_switch = @save_optimizer_switch;
+/* E.2 Outer query without tables, always uses IN-TO-EXISTS. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	t2	index_subquery	it2i4,it2i1,it2i3	it2i1	8	const	5	Using index; Using where
+select '1 - 03' in (select b1 from t2 where b1 > '0');
+'1 - 03' in (select b1 from t2 where b1 > '0')
+1
+/* E.3 Subqueries without tables. */
+explain
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i1,it1i2,it1i3	it1i3	16	NULL	3	Using where; Using index
+Warnings:
+Note	1249	Select 2 was reduced during optimization
+select a1 from t1 where a1 in (select '1 - 03') or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+UNION subqueries are currently limited to only use IN-TO-EXISTS.
+explain
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	8	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+3	DEPENDENT UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
+select a1 from t1 where a1 in (select '1 - 03' UNION select '1 - 02');
+a1
+1 - 02
+/* E.4 optimize_cond detects FALSE where/having clause. */
+explain
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	it1i2	it1i3	16	NULL	3	Using where; Using index
+2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
+select a1 from t1 where a1 in (select b1 from t2 where b1 = b2 and b2 = '1 - 03' and b1 = '1 - 02' ) or a2 < '9';
+a1
+1 - 00
+1 - 01
+1 - 02
+/* E.5 opt_sum_query detects no matching min/max row or substitutes MIN/MAX with a const. */
+TODO this test produces wrong result due to missing logic to handle the case
+when JOIN::optimize detects an empty subquery result.
+explain
+select a1 from t1 where a1 in (select max(b1) from t2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	8	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
+select a1 from t1 where a1 in (select max(b1) from t2);
+a1
+
+explain
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	index	NULL	it1i1	8	NULL	3	Using where; Using index
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No matching min/max row
+select a1 from t1 where a1 in (select max(b1) from t2 where b1 = '7 - 02');
+a1
+/* E.6 make_join_select detects impossible WHERE. *
+TODO
+/* E.7 constant optimization detects "no matching row in const table". */
+TODO
+/* E.8 Impossible WHERE noticed after reading const tables. */
+explain
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	DEPENDENT SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+select '1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0');
+'1 - 03' in (select b1 from t2 where b1 > '0' and b1 < '0')
+0
+
+/* F. UPDATE/DELETE with subqueries. */
+
+TODO
+
+call set_all_columns_nullable();
+drop procedure make_t1_indexes;
+drop procedure make_t2_indexes;
+drop procedure remove_t1_indexes;
+drop procedure remove_t2_indexes;
+drop procedure add_materialization_data;
+drop procedure delete_materialization_data;
+drop procedure set_all_columns_not_null;
+drop procedure set_all_columns_nullable;
+drop table t1, t2, t1_1024, t2_1024;
+#
+# LP BUG#643424 valgrind warning in choose_subquery_plan()
+#
+CREATE TABLE t1 (
+pk int(11) NOT NULL AUTO_INCREMENT,
+c1 int(11) DEFAULT NULL,
+c2 int(11) DEFAULT NULL,
+PRIMARY KEY (pk),
+KEY c2 (c2));
+INSERT INTO t1 VALUES (1,NULL,2);
+INSERT INTO t1 VALUES (2,7,9);
+INSERT INTO t1 VALUES (9,NULL,8);
+CREATE TABLE t2 (
+pk int(11) NOT NULL AUTO_INCREMENT,
+c1 int(11) DEFAULT NULL,
+c2 int(11) DEFAULT NULL,
+PRIMARY KEY (pk),
+KEY c2 (c2));
+INSERT INTO t2 VALUES (1,1,7);
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch='materialization=on,in_to_exists=on,semijoin=off';
+SELECT pk FROM t1 WHERE (c2, c1) IN (SELECT c2, c2 FROM t2);
+pk
+set session optimizer_switch=@save_optimizer_switch;
+drop table t1, t2;
+#
+# LP BUG#652727 Crash in create_ref_for_key()
+#
+CREATE TABLE t2 (
+pk int(11) NOT NULL AUTO_INCREMENT,
+c1 int(11) DEFAULT NULL,
+PRIMARY KEY (pk));
+INSERT INTO t2 VALUES (10,7);
+INSERT INTO t2 VALUES (11,1);
+INSERT INTO t2 VALUES (17,NULL);
+CREATE TABLE t1 (
+pk int(11) NOT NULL AUTO_INCREMENT,
+c1 int(11) DEFAULT NULL,
+PRIMARY KEY (pk));
+INSERT INTO t1 VALUES (15,1);
+INSERT INTO t1 VALUES (19,NULL);
+CREATE TABLE t3 (c2 int(11) DEFAULT NULL, KEY c2 (c2));
+INSERT INTO t3 VALUES (1);
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch='materialization=on,in_to_exists=on,semijoin=off';
+SELECT c2
+FROM t3
+WHERE (2, 6) IN (SELECT t1.c1, t1.c1 FROM t1 STRAIGHT_JOIN t2 ON t2.pk = t1.pk);
+c2
+set session optimizer_switch=@save_optimizer_switch;
+drop table t1, t2, t3;
diff --git a/mysql-test/t/subselect3.test b/mysql-test/t/subselect3.test
index a621c4c776c..3f63149ce96 100644
--- a/mysql-test/t/subselect3.test
+++ b/mysql-test/t/subselect3.test
@@ -681,7 +681,8 @@ SELECT a, ROW(11, 12) = (SELECT a, 12), ROW(11, 12) IN (SELECT a, 12) FROM t1;
 # The x alias is used below to workaround bug #40674.
 # Regression tests for sum function on outer column in subselect from dual:
 SELECT a AS x, ROW(11, 12) = (SELECT MAX(x), 22), ROW(11, 12) IN (SELECT MAX(x), 22) FROM t1;
---echo # 2nd and 3rd columns should be same for x == 11 only
+--echo # 2nd and 3rd columns should be same
+EXPLAIN SELECT a AS x, ROW(11, 12) = (SELECT MAX(x), 12), ROW(11, 12) IN (SELECT MAX(x), 12) FROM t1;
 SELECT a AS x, ROW(11, 12) = (SELECT MAX(x), 12), ROW(11, 12) IN (SELECT MAX(x), 12) FROM t1;
 
 DROP TABLE t1;
diff --git a/mysql-test/t/subselect_mat.test b/mysql-test/t/subselect_mat.test
index 0209bf66a57..9a3e8352a2c 100644
--- a/mysql-test/t/subselect_mat.test
+++ b/mysql-test/t/subselect_mat.test
@@ -48,7 +48,7 @@ insert into t2i select * from t2;
 insert into t3i select * from t3;
 
 # force the use of materialization
-set @@optimizer_switch='semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 
 /******************************************************************************
 * Simple tests.
@@ -111,22 +111,22 @@ select * from t1 where (a1, a2) in (select b1, min(b2) from t2i limit 1,1);
 
 # test re-optimization/re-execution with different execution methods
 # prepare once, exec with different modes
-set @@optimizer_switch='default,semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=on';
 prepare st1 from
 "select * from t1 where (a1, a2) in (select b1, min(b2) from t2 where b1 > '0' group by b1)";
-set @@optimizer_switch='default,materialization=off';
+set @@optimizer_switch='materialization=off,in_to_exists=on,semijoin=on';
 execute st1;
-set @@optimizer_switch='default,semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=on';
 execute st1;
 
-set @@optimizer_switch='default,materialization=off';
+set @@optimizer_switch='materialization=off,in_to_exists=on,semijoin=on';
 prepare st1 from
 "select * from t1 where (a1, a2) in (select b1, min(b2) from t2 where b1 > '0' group by b1)";
-set @@optimizer_switch='default,semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 execute st1;
-set @@optimizer_switch='default,materialization=off';
+set @@optimizer_switch='materialization=off,in_to_exists=on,semijoin=on';
 execute st1;
-set @@optimizer_switch='default,semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 
 # materialize the result of ORDER BY
 # non-indexed fields
@@ -327,7 +327,7 @@ select * from t1 order by (select col from columns limit 1);
   Test that BLOBs are not materialized (except when arguments of some functions).
 */
 # force materialization to be always considered
-set @@optimizer_switch='semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 set @prefix_len = 6;
 
 # BLOB == 16 (small blobs that could be stored in HEAP tables)
@@ -680,7 +680,7 @@ insert into t2bit values (b'001', b'101');
 insert into t2bit values (b'010', b'110');
 insert into t2bit values (b'110', b'111');
 
-set @@optimizer_switch='semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 
 explain extended select bin(a1), bin(a2)
 from t1bit
@@ -718,7 +718,7 @@ drop table t1, t2, t3, t1i, t2i, t3i, columns;
 /******************************************************************************
 * Test the cache of the left operand of IN.
 ******************************************************************************/
-set @@optimizer_switch='semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 
 # Test that default values of Cached_item are not used for comparison
 create table t1 (s1 int);
@@ -812,23 +812,28 @@ drop table t2;
 create table t1 (a1 int key);
 create table t2 (b1 int);
 insert into t1 values (5);
-
+-- echo Only the last query returns correct result. Filed as BUG#40037.
 # Query with group by, executed via materialization
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 explain select min(a1) from t1 where 7 in (select b1 from t2 group by b1);
 select min(a1) from t1 where 7 in (select b1 from t2 group by b1);
 # Query with group by, executed via IN=>EXISTS
-set @@optimizer_switch='default,materialization=off';
+set @@optimizer_switch='materialization=off,in_to_exists=on,semijoin=off';
 explain select min(a1) from t1 where 7 in (select b1 from t2 group by b1);
 select min(a1) from t1 where 7 in (select b1 from t2 group by b1);
 
 # Executed with materialization
-set @@optimizer_switch='default,semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
+explain select min(a1) from t1 where 7 in (select b1 from t2);
+select min(a1) from t1 where 7 in (select b1 from t2);
+# Executed via IN=>EXISTS
+set @@optimizer_switch='materialization=off,in_to_exists=on,semijoin=off';
 explain select min(a1) from t1 where 7 in (select b1 from t2);
 select min(a1) from t1 where 7 in (select b1 from t2);
 # Executed with semi-join. Notice, this time we get a different result (NULL).
-# This is the only correct result of all four queries. This difference is
+# This is the only correct result of all five queries. This difference is
 # filed as BUG#40037.
-set @@optimizer_switch='default,materialization=off';
+set @@optimizer_switch='materialization=off,in_to_exists=off,semijoin=on';
 explain select min(a1) from t1 where 7 in (select b1 from t2);
 select min(a1) from t1 where 7 in (select b1 from t2);
 drop table t1,t2;
@@ -840,7 +845,7 @@ create table t1 (a char(2), b varchar(10));
 insert into t1 values ('a',  'aaa');
 insert into t1 values ('aa', 'aaaa');
 
-set @@optimizer_switch='default,semijoin=off';
+set @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=off';
 explain select a,b from t1 where b in (select a from t1);
 select a,b from t1 where b in (select a from t1);
 prepare st1 from "select a,b from t1 where b in (select a from t1)";
@@ -861,7 +866,7 @@ CREATE TABLE t2 LIKE t1;
 INSERT INTO t2 VALUES (1, 1.789);
 INSERT INTO t2 VALUES (13, 1.454);
 
-SET @@optimizer_switch='default,semijoin=on,materialization=on';
+SET @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=on';
 EXPLAIN SELECT COUNT(*) FROM t1 WHERE (f1,f2) IN (SELECT f1,f2 FROM t2);
 SELECT COUNT(*) FROM t1 WHERE (f1,f2) IN (SELECT f1,f2 FROM t2);
 
@@ -883,7 +888,7 @@ INSERT INTO t1 VALUES (1,'o','ffff','ffff','ffoo'),(2,'f','ffff','ffff','ffff');
 CREATE TABLE t2 LIKE t1;
 INSERT INTO t2 VALUES (1,'i','iiii','iiii','iiii'),(2,'f','ffff','ffff','ffff');
 
-SET @@optimizer_switch='default,semijoin=on,materialization=on';
+SET @@optimizer_switch='materialization=on,in_to_exists=off,semijoin=on';
 EXPLAIN SELECT pk FROM t1 WHERE (a) IN (SELECT a FROM t2 WHERE pk > 0);
 SELECT pk FROM t1 WHERE (a) IN (SELECT a FROM t2 WHERE pk > 0);
 SELECT pk FROM t1 WHERE (b,c,d) IN (SELECT b,c,d FROM t2 WHERE pk > 0);
@@ -900,7 +905,7 @@ create table t3(i int);
 insert into t3 values (1), (2), (3), (4), (5), (6), (7), (8), (9), (10);
 select * from t1 where t1.i in (select t2.i from t2 join t3 where t2.i + t3.i = 5);
 set @save_optimizer_switch=@@optimizer_switch;
-set session optimizer_switch='materialization=off';
+set session optimizer_switch='materialization=off,in_to_exists=on';
 select * from t1 where t1.i in (select t2.i from t2 join t3 where t2.i + t3.i = 5);
 set session optimizer_switch=@save_optimizer_switch;
 drop table t1, t2, t3;
diff --git a/mysql-test/t/subselect_mat_cost.test b/mysql-test/t/subselect_mat_cost.test
new file mode 100644
index 00000000000..b817c05f7d4
--- /dev/null
+++ b/mysql-test/t/subselect_mat_cost.test
@@ -0,0 +1,271 @@
+#
+# Tets of cost-based choice between the materialization and in-to-exists
+# subquery execution strategies (MWL#89)
+#
+
+--disable_warnings
+drop table if exists t1, t2, t1_1024, t2_1024;
+drop procedure if exists make_t1_indexes;
+drop procedure if exists make_t2_indexes;
+drop procedure if exists remove_t1_indexes;
+drop procedure if exists remove_t2_indexes;
+drop procedure if exists add_materialization_data;
+drop procedure if exists delete_materialization_data;
+drop procedure if exists set_all_columns_not_null;
+drop procedure if exists set_all_columns_nullable;
+--enable_warnings
+
+create table t1 (a1 char(8), a2 char(8), a3 char(8), a4 int);
+insert into t1 values ('1 - 00', '2 - 00', '3 - 00', 0);
+insert into t1 values ('1 - 01', '2 - 01', '3 - 01', 1);
+insert into t1 values ('1 - 02', '2 - 02', '3 - 02', 2);
+
+create table t2 (b1 char(8), b2 char(8), b3 char(8), b4 int);
+insert into t2 values ('1 - 01', '2 - 01', '3 - 01', 1);
+insert into t2 values ('1 - 01', '2 - 01', '3 - 02', 2);
+insert into t2 values ('1 - 02', '2 - 02', '3 - 03', 3);
+insert into t2 values ('1 - 02', '2 - 02', '3 - 04', 4);
+insert into t2 values ('1 - 03', '2 - 03', '3 - 05', 5);
+
+create table t1_1024 (a1 blob(1024), a2 blob(1024));
+insert into t1_1024 values (concat('1 - 00', repeat('x', 1018)), concat('2 - 00', repeat('x', 1018)));
+insert into t1_1024 values (concat('1 - 01', repeat('x', 1018)), concat('2 - 01', repeat('x', 1018)));
+
+create table t2_1024 (b1 blob(1024), b2 blob(1024));
+insert into t2_1024 values (concat('1 - 01', repeat('x', 1018)), concat('2 - 01', repeat('x', 1018)));
+insert into t2_1024 values (concat('1 - 02', repeat('x', 1018)), concat('2 - 02', repeat('x', 1018)));
+insert into t2_1024 values (concat('1 - 03', repeat('x', 1018)), concat('2 - 03', repeat('x', 1018)));
+insert into t2_1024 values (concat('1 - 04', repeat('x', 1018)), concat('2 - 04', repeat('x', 1018)));
+
+delimiter |;
+create procedure make_t1_indexes()
+begin
+  create index it1i1 on t1 (a1);
+  create index it1i2 on t1 (a2);
+  create index it1i3 on t1 (a1, a2);
+  create index it1_1024i1 on t1_1024 (a1(6));
+  create index it1_1024i2 on t1_1024 (a2(6));
+  create index it1_1024i3 on t1_1024 (a1(6), a2(6));
+end|
+
+create procedure make_t2_indexes()
+begin
+  create index it2i1 on t2 (b1);
+  create index it2i2 on t2 (b2);
+  create index it2i3 on t2 (b1, b2);
+  create unique index it2i4 on t2 (b1, b2, b3);
+  create index it2_1024i1 on t2_1024 (b1(6));
+  create index it2_1024i2 on t2_1024 (b2(6));
+  create index it2_1024i3 on t2_1024 (b1(6), b2(6));
+end|
+
+create procedure remove_t1_indexes()
+begin
+  drop index it1i1 on t1;
+  drop index it1i2 on t1;
+  drop index it1i3 on t1;
+  drop index it1_1024i1 on t1_1024;
+  drop index it1_1024i2 on t1_1024;
+  drop index it1_1024i3 on t1_1024;
+end|
+
+create procedure remove_t2_indexes()
+begin
+  drop index it2i1 on t2;
+  drop index it2i2 on t2;
+  drop index it2i3 on t2;
+  drop index it2i4 on t2;
+  drop index it2_1024i1 on t2_1024;
+  drop index it2_1024i2 on t2_1024;
+  drop index it2_1024i3 on t2_1024;
+end|
+
+create procedure add_materialization_data()
+begin
+insert into t1 values ('1 - 03', '2 - 03', '3 - 03', 3);
+insert into t1 values ('1 - 04', '2 - 04', '3 - 04', 4);
+insert into t1 values ('1 - 05', '2 - 05', '3 - 05', 5);
+insert into t1 values ('1 - 06', '2 - 06', '3 - 06', 6);
+insert into t1 values ('1 - 07', '2 - 07', '3 - 07', 7);
+insert into t1_1024 values (concat('1 - 03', repeat('x', 1018)), concat('2 - 03', repeat('x', 1018)));
+end|
+
+create procedure delete_materialization_data()
+begin
+delete from t1 where a1 >= '1 - 03';
+delete from t1_1024 where a1 >= '1 - 03';
+end|
+
+create procedure set_all_columns_not_null()
+begin
+alter table t1 modify a1 char(8) not null, modify a2 char(8) not null, modify a3 char(8) not null;
+alter table t2 modify b1 char(8) not null, modify b2 char(8) not null, modify b3 char(8) not null;
+end|
+
+create procedure set_all_columns_nullable()
+begin
+alter table t1 modify a1 char(8) null, modify a2 char(8) null, modify a3 char(8) null;
+alter table t2 modify b1 char(8) null, modify b2 char(8) null, modify b3 char(8) null;
+end|
+
+delimiter ;|
+-- echo
+
+-- echo /******************************************************************************
+-- echo 1. Both materialization and in-to-exists are ON, make a cost-based choice.
+-- echo ******************************************************************************/
+set @@optimizer_switch='materialization=on,in_to_exists=on';
+-- echo 
+-- echo /* 1.1 In-to-exists is cheaper */
+call make_t1_indexes();
+
+-- echo /* 1.1.1 non-indexed table access */
+-- source include/subselect_mat_cost.inc
+
+-- echo /* 1.1.2 indexed table access, nullabale columns. */
+call make_t2_indexes();
+-- source include/subselect_mat_cost.inc
+
+-- echo /* 1.1.3 indexed table access, non-nullabale columns. */
+call set_all_columns_not_null();
+-- source include/subselect_mat_cost.inc
+call set_all_columns_nullable();
+
+-- echo 
+-- echo /* 1.2 Materialization is cheaper */
+# make materialization cheaper
+call add_materialization_data();
+call remove_t1_indexes();
+
+-- echo /* 1.2.1 non-indexed table access */
+call remove_t2_indexes();
+-- source include/subselect_mat_cost.inc
+
+-- echo /* 1.2.2 indexed table access, nullabale columns. */
+call make_t2_indexes();
+-- source include/subselect_mat_cost.inc
+
+-- echo /* 1.2.3 indexed table access, non-nullabale columns. */
+call set_all_columns_not_null();
+-- source include/subselect_mat_cost.inc
+call set_all_columns_nullable();
+
+
+-- echo /******************************************************************************
+-- echo 2. Materialization is OFF, in-to-exists is ON, materialization is cheaper.
+-- echo ******************************************************************************/
+set @@optimizer_switch='materialization=off,in_to_exists=on';
+
+-- echo /* 2.1 non-indexed table access */
+call remove_t2_indexes();
+-- source include/subselect_mat_cost.inc
+
+-- echo /* 2.2 indexed table access, nullabale columns. */
+call make_t2_indexes();
+-- source include/subselect_mat_cost.inc
+
+-- echo /* 2.3 indexed table access, non-nullabale columns. */
+call set_all_columns_not_null();
+-- source include/subselect_mat_cost.inc
+call set_all_columns_nullable();
+
+
+-- echo /******************************************************************************
+-- echo 3. Materialization is ON, in-to-exists is OFF, in-to-exists is cheaper.
+-- echo ******************************************************************************/
+set @@optimizer_switch='materialization=on,in_to_exists=off';
+# make IN-TO-EXISTS cheaper
+call delete_materialization_data();
+call make_t1_indexes();
+
+-- echo /* 3.1 non-indexed table access */
+call remove_t2_indexes();
+-- source include/subselect_mat_cost.inc
+
+-- echo /* 3.2 indexed table access, nullabale columns. */
+call make_t2_indexes();
+-- source include/subselect_mat_cost.inc
+
+-- echo /* 3.3 indexed table access, non-nullabale columns. */
+call set_all_columns_not_null();
+-- source include/subselect_mat_cost.inc
+call set_all_columns_nullable();
+
+
+drop procedure make_t1_indexes;
+drop procedure make_t2_indexes;
+drop procedure remove_t1_indexes;
+drop procedure remove_t2_indexes;
+drop procedure add_materialization_data;
+drop procedure delete_materialization_data;
+drop procedure set_all_columns_not_null;
+drop procedure set_all_columns_nullable;
+drop table t1, t2, t1_1024, t2_1024;
+
+--echo #
+--echo # LP BUG#643424 valgrind warning in choose_subquery_plan()
+--echo #
+
+CREATE TABLE t1 (
+  pk int(11) NOT NULL AUTO_INCREMENT,
+  c1 int(11) DEFAULT NULL,
+  c2 int(11) DEFAULT NULL,
+  PRIMARY KEY (pk),
+  KEY c2 (c2));
+
+INSERT INTO t1 VALUES (1,NULL,2);
+INSERT INTO t1 VALUES (2,7,9);
+INSERT INTO t1 VALUES (9,NULL,8);
+
+CREATE TABLE t2 (
+  pk int(11) NOT NULL AUTO_INCREMENT,
+  c1 int(11) DEFAULT NULL,
+  c2 int(11) DEFAULT NULL,
+  PRIMARY KEY (pk),
+  KEY c2 (c2));
+
+INSERT INTO t2 VALUES (1,1,7);
+
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch='materialization=on,in_to_exists=on,semijoin=off';
+
+SELECT pk FROM t1 WHERE (c2, c1) IN (SELECT c2, c2 FROM t2);
+
+set session optimizer_switch=@save_optimizer_switch;
+
+drop table t1, t2;
+
+
+--echo #
+--echo # LP BUG#652727 Crash in create_ref_for_key()
+--echo #
+
+CREATE TABLE t2 (
+  pk int(11) NOT NULL AUTO_INCREMENT,
+  c1 int(11) DEFAULT NULL,
+  PRIMARY KEY (pk));
+
+INSERT INTO t2 VALUES (10,7);
+INSERT INTO t2 VALUES (11,1);
+INSERT INTO t2 VALUES (17,NULL);
+
+CREATE TABLE t1 (
+  pk int(11) NOT NULL AUTO_INCREMENT,
+  c1 int(11) DEFAULT NULL,
+  PRIMARY KEY (pk));
+
+INSERT INTO t1 VALUES (15,1);
+INSERT INTO t1 VALUES (19,NULL);
+
+CREATE TABLE t3 (c2 int(11) DEFAULT NULL, KEY c2 (c2));
+INSERT INTO t3 VALUES (1);
+
+set @save_optimizer_switch=@@optimizer_switch;
+set @@optimizer_switch='materialization=on,in_to_exists=on,semijoin=off';
+
+SELECT c2
+FROM t3
+WHERE (2, 6) IN (SELECT t1.c1, t1.c1 FROM t1 STRAIGHT_JOIN t2 ON t2.pk = t1.pk);
+
+set session optimizer_switch=@save_optimizer_switch;
+drop table t1, t2, t3;
diff --git a/sql/item.h b/sql/item.h
index 2158206441e..9adea4ec726 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -948,6 +948,8 @@ public:
   virtual bool register_field_in_read_map(uchar *arg) { return 0; }
   virtual bool enumerate_field_refs_processor(uchar *arg) { return 0; }
   virtual bool mark_as_eliminated_processor(uchar *arg) { return 0; }
+  virtual bool eliminate_subselect_processor(uchar *arg) { return 0; }
+  virtual bool set_fake_select_as_master_processor(uchar *arg) { return 0; }
 
   /* To call bool function for all arguments */
   struct bool_func_call_args
diff --git a/sql/item_cmpfunc.cc b/sql/item_cmpfunc.cc
index 2b331fd4bf3..88bc5707dbe 100644
--- a/sql/item_cmpfunc.cc
+++ b/sql/item_cmpfunc.cc
@@ -1985,6 +1985,18 @@ Item *Item_in_optimizer::transform(Item_transformer transformer, uchar *argument
 }
 
 
+bool Item_in_optimizer::is_expensive_processor(uchar *arg)
+{
+  return args[1]->is_expensive_processor(arg);
+}
+
+
+bool Item_in_optimizer::is_expensive()
+{
+  return args[1]->is_expensive();
+}
+
+
 longlong Item_func_eq::val_int()
 {
   DBUG_ASSERT(fixed == 1);
@@ -4650,12 +4662,6 @@ Item *and_expressions(Item *a, Item *b, Item **org_item)
 longlong Item_func_isnull::val_int()
 {
   DBUG_ASSERT(fixed == 1);
-  /*
-    Handle optimization if the argument can't be null
-    This has to be here because of the test in update_used_tables().
-  */
-  if (!used_tables_cache && !with_subselect)
-    return cached_value;
   return args[0]->is_null() ? 1: 0;
 }
 
@@ -4663,12 +4669,6 @@ longlong Item_is_not_null_test::val_int()
 {
   DBUG_ASSERT(fixed == 1);
   DBUG_ENTER("Item_is_not_null_test::val_int");
-  if (!used_tables_cache && !with_subselect)
-  {
-    owner->was_null|= (!cached_value);
-    DBUG_PRINT("info", ("cached: %ld", (long) cached_value));
-    DBUG_RETURN(cached_value);
-  }
   if (args[0]->is_null())
   {
     DBUG_PRINT("info", ("null"));
@@ -4685,19 +4685,9 @@ longlong Item_is_not_null_test::val_int()
 void Item_is_not_null_test::update_used_tables()
 {
   if (!args[0]->maybe_null)
-  {
     used_tables_cache= 0;			/* is always true */
-    cached_value= (longlong) 1;
-  }
   else
-  {
     args[0]->update_used_tables();
-    if (!(used_tables_cache=args[0]->used_tables()) && !with_subselect)
-    {
-      /* Remember if the value is always NULL or never NULL */
-      cached_value= (longlong) !args[0]->is_null();
-    }
-  }
 }
 
 
@@ -5373,7 +5363,7 @@ Item *Item_func_nop_all::neg_transformer(THD *thd)
   /* "NOT (e $cmp$ ANY (SELECT ...)) -> e $rev_cmp$" ALL (SELECT ...) */
   Item_func_not_all *new_item= new Item_func_not_all(args[0]);
   Item_allany_subselect *allany= (Item_allany_subselect*)args[0];
-  allany->func= allany->func_creator(FALSE);
+  allany->create_comp_func(FALSE);
   allany->all= !allany->all;
   allany->upper_item= new_item;
   return new_item;
@@ -5385,7 +5375,7 @@ Item *Item_func_not_all::neg_transformer(THD *thd)
   Item_func_nop_all *new_item= new Item_func_nop_all(args[0]);
   Item_allany_subselect *allany= (Item_allany_subselect*)args[0];
   allany->all= !allany->all;
-  allany->func= allany->func_creator(TRUE);
+  allany->create_comp_func(TRUE);
   allany->upper_item= new_item;
   return new_item;
 }
@@ -5668,6 +5658,9 @@ longlong Item_equal::val_int()
   Item_field *item_field;
   if (cond_false)
     return 0;
+  /* If there is a single constant and no fields, the equality is TRUE. */
+  if (const_item && !fields.elements)
+    return 1;
   List_iterator_fast<Item_field> it(fields);
   Item *item= const_item ? const_item : it++;
   if ((null_value= item->is_null()))
@@ -5688,6 +5681,15 @@ longlong Item_equal::val_int()
 void Item_equal::fix_length_and_dec()
 {
   Item *item= get_first(NULL);
+  if (!item)
+  {
+    /*
+      If there are no fields, there must be at least a constant, in which
+      case Item_equal::val_int evaluates to TRUE.
+    */
+    DBUG_ASSERT(const_item);
+    return;
+  }
   eval_item= cmp_item::get_comparator(item->result_type(),
                                       item->collation.collation);
 }
diff --git a/sql/item_cmpfunc.h b/sql/item_cmpfunc.h
index 8a62f69de1f..a60a3b00d8b 100644
--- a/sql/item_cmpfunc.h
+++ b/sql/item_cmpfunc.h
@@ -266,6 +266,8 @@ public:
   void keep_top_level_cache();
   Item *transform(Item_transformer transformer, uchar *arg);
   virtual Item *expr_cache_insert_transformer(uchar *thd_arg);
+  bool is_expensive_processor(uchar *arg);
+  bool is_expensive();
 };
 
 class Comp_creator
@@ -1303,8 +1305,6 @@ public:
 
 class Item_func_isnull :public Item_bool_func
 {
-protected:
-  longlong cached_value;
 public:
   Item_func_isnull(Item *a) :Item_bool_func(a) {}
   longlong val_int();
@@ -1322,18 +1322,9 @@ public:
     {
       used_tables_cache= 0;			/* is always false */
       const_item_cache= 1;
-      cached_value= (longlong) 0;
     }
     else
-    {
       args[0]->update_used_tables();
-      if ((const_item_cache= !(used_tables_cache= args[0]->used_tables()) &&
-          !with_subselect))
-      {
-	/* Remember if the value is always NULL or never NULL */
-	cached_value= (longlong) args[0]->is_null();
-      }
-    }
   }
   table_map not_null_tables() const { return 0; }
   optimize_type select_optimize() const { return OPTIMIZE_NULL; }
diff --git a/sql/item_subselect.cc b/sql/item_subselect.cc
index 8a17ce73556..bd6c3c62f7b 100644
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@@ -36,8 +36,8 @@ Item_subselect::Item_subselect():
   Item_result_field(), value_assigned(0), thd(0), substitution(0),
   expr_cache(0), engine(0), old_engine(0), used_tables_cache(0),
   have_to_be_excluded(0), const_item_cache(1), inside_first_fix_fields(0),
-  done_first_fix_fields(FALSE), eliminated(FALSE), engine_changed(0),
-  changed(0), is_correlated(FALSE)
+  done_first_fix_fields(FALSE), forced_const(FALSE), eliminated(FALSE),
+  engine_changed(0), changed(0), is_correlated(FALSE)
 {
   with_subselect= 1;
   reset();
@@ -60,7 +60,7 @@ void Item_subselect::init(st_select_lex *select_lex,
   DBUG_ENTER("Item_subselect::init");
   DBUG_PRINT("enter", ("select_lex: 0x%lx", (long) select_lex));
   unit= select_lex->master_unit();
-
+  thd= unit->thd;
   if (unit->item)
   {
     /*
@@ -121,6 +121,7 @@ void Item_subselect::cleanup()
   reset();
   value_assigned= 0;
   expr_cache= 0;
+  forced_const= FALSE;
   DBUG_VOID_RETURN;
 }
 
@@ -158,7 +159,9 @@ void Item_in_subselect::cleanup()
     left_expr_cache= NULL;
   }
   first_execution= TRUE;
-  is_constant= FALSE;
+  if (in_strategy & SUBS_MATERIALIZATION)
+    in_strategy= 0;
+  pushed_cond_guards= NULL;
   Item_subselect::cleanup();
   DBUG_VOID_RETURN;
 }
@@ -166,6 +169,7 @@ void Item_in_subselect::cleanup()
 Item_subselect::~Item_subselect()
 {
   delete engine;
+  engine= NULL;
 }
 
 Item_subselect::trans_res
@@ -183,7 +187,8 @@ bool Item_subselect::fix_fields(THD *thd_param, Item **ref)
   bool res;
 
   DBUG_ASSERT(fixed == 0);
-  engine->set_thd((thd= thd_param));
+  DBUG_ASSERT(thd == thd_param); /* thd can't change during execution. */
+  engine->set_thd(thd);
   if (!done_first_fix_fields)
   {
     done_first_fix_fields= TRUE;
@@ -206,11 +211,7 @@ bool Item_subselect::fix_fields(THD *thd_param, Item **ref)
   {
     // all transformation is done (used by prepared statements)
     changed= 1;
-  inside_first_fix_fields= FALSE;
-
-
-    // all transformation is done (used by prepared statements)
-    changed= 1;
+    inside_first_fix_fields= FALSE;
 
     /*
       Substitute the current item with an Item_in_optimizer that was
@@ -220,11 +221,14 @@ bool Item_subselect::fix_fields(THD *thd_param, Item **ref)
     */
     if (substitution)
     {
-      // did we changed top item of WHERE condition
+      /*
+        If the top item of the WHERE/HAVING condition changed,
+        set correct WHERE/HAVING for PS.
+      */
       if (unit->outer_select()->where == (*ref))
-	unit->outer_select()->where= substitution; // correct WHERE for PS
+        thd->change_item_tree(&(unit->outer_select()->where), substitution);
       else if (unit->outer_select()->having == (*ref))
-	unit->outer_select()->having= substitution; // correct HAVING for PS
+        thd->change_item_tree(&(unit->outer_select()->having), substitution);
 
       (*ref)= substitution;
       substitution->name= name;
@@ -284,6 +288,73 @@ bool Item_subselect::mark_as_eliminated_processor(uchar *arg)
 }
 
 
+/**
+  Remove a subselect item from its unit so that the unit no longer
+  represents a subquery.
+
+  @param arg  unused parameter
+
+  @return
+    FALSE to force the evaluation of the processor for the subsequent items.
+*/
+
+bool Item_subselect::eliminate_subselect_processor(uchar *arg)
+{
+  unit->item= NULL;
+  unit->exclude_from_tree();
+  eliminated= TRUE;
+  return FALSE;
+}
+
+
+/**
+  Adjust the master select of the subquery to be the fake_select which
+  represents the whole UNION right above the subquery, instead of the
+  last query of the UNION.
+
+  @param arg  pointer to the fake select
+
+  @return
+    FALSE to force the evaluation of the processor for the subsequent items.
+*/
+
+bool Item_subselect::set_fake_select_as_master_processor(uchar *arg)
+{
+  SELECT_LEX *fake_select= (SELECT_LEX*) arg;
+  /*
+    Move the st_select_lex_unit of a subquery from a global ORDER BY clause to
+    become a direct child of the fake_select of a UNION. In this way the
+    ORDER BY is applied to the temporary table that contains the result of the
+    whole UNION, and all columns in the subquery are resolved against this table.
+
+    Apply the transformation only for immediate child subqueries of a
+    UNION query.
+  */
+  if (unit->outer_select()->master_unit()->fake_select_lex == fake_select)
+  {
+    /*
+      Set the master of the subquery to be the fake select (i.e. the whole UNION),
+      instead of the last query in the UNION.
+      TODO:
+      This is a hack, instead we should call: unit->include_down(fake_select);
+      However, this call results in an infinite loop where
+      some_select_lex->master == some_select_lex.
+    */
+    unit->set_master(fake_select);
+    /* Adjust the name resolution context hierarchy accordingly. */
+    for (SELECT_LEX *sl= unit->first_select(); sl; sl= sl->next_select())
+      sl->context.outer_context= &(fake_select->context);
+    /*
+      Undo Item_subselect::eliminate_subselect_processor because at that phase
+      we don't know yet that the ORDER clause will be moved to the fake select.
+    */
+    unit->item= this;
+    eliminated= FALSE;
+  }
+  return FALSE;
+}
+
+
 bool Item_subselect::mark_as_dependent(THD *thd, st_select_lex *select, 
                                        Item *item)
 {
@@ -558,7 +629,7 @@ bool Item_in_subselect::exec()
     - on a cost-based basis, that takes into account the cost of a cache
       lookup, the cache hit rate, and the savings per cache hit.
   */
-  if (!left_expr_cache && exec_method == MATERIALIZATION)
+  if (!left_expr_cache && (in_strategy & SUBS_MATERIALIZATION))
     init_left_expr_cache();
 
   /*
@@ -611,12 +682,15 @@ Item *Item_subselect::get_tmp_table_item(THD *thd_arg)
 
 void Item_subselect::update_used_tables()
 {
-  recalc_used_tables(parent_select, FALSE);
-  if (!engine->uncacheable())
+  if (!forced_const)
   {
-    // did all used tables become static?
-    if (!(used_tables_cache & ~engine->upper_select_const_tables()))
-      const_item_cache= 1;
+    recalc_used_tables(parent_select, FALSE);
+    if (!engine->uncacheable())
+    {
+      // did all used tables become static?
+      if (!(used_tables_cache & ~engine->upper_select_const_tables()))
+        const_item_cache= 1;
+    }
   }
 }
 
@@ -682,7 +756,7 @@ Item_maxmin_subselect::Item_maxmin_subselect(THD *thd_param,
     of Items belonged to subquery, which will be not repeated
   */
   used_tables_cache= parent->get_used_tables_cache();
-  const_item_cache= parent->get_const_item_cache();
+  const_item_cache= parent->const_item();
 
   /*
     this subquery always creates during preparation, so we can assign
@@ -720,8 +794,7 @@ void Item_maxmin_subselect::print(String *str, enum_query_type query_type)
 
 void Item_singlerow_subselect::reset()
 {
-  eliminated= FALSE;
-  null_value= 1;
+  Item_subselect::reset();
   if (value)
     value->null_value= 1;
 }
@@ -1015,11 +1088,11 @@ bool Item_in_subselect::test_limit(st_select_lex_unit *unit_arg)
 Item_in_subselect::Item_in_subselect(Item * left_exp,
 				     st_select_lex *select_lex):
   Item_exists_subselect(), left_expr_cache(0), first_execution(TRUE),
-  is_constant(FALSE), optimizer(0), pushed_cond_guards(NULL),
-  exec_method(NOT_TRANSFORMED), upper_item(0)
+  optimizer(0), pushed_cond_guards(NULL), in_strategy(0), upper_item(0)
 {
   DBUG_ENTER("Item_in_subselect::Item_in_subselect");
   left_expr= left_exp;
+  func= &eq_creator;
   init(select_lex, new select_exists_subselect(this));
   max_columns= UINT_MAX;
   maybe_null= 1;
@@ -1249,7 +1322,7 @@ bool Item_in_subselect::val_bool()
 {
   DBUG_ASSERT(fixed == 1);
   null_value= 0;
-  if (is_constant)
+  if (forced_const)
     return value;
   if (exec())
   {
@@ -1289,59 +1362,37 @@ my_decimal *Item_in_subselect::val_decimal(my_decimal *decimal_value)
 }
 
 
-/* 
-  Rewrite a single-column IN/ALL/ANY subselect
+/**
+  Rewrite a single-column IN/ALL/ANY subselect.
 
-  SYNOPSIS
-    Item_in_subselect::single_value_transformer()
-      join  Join object of the subquery (i.e. 'child' join).
-      func  Subquery comparison creator
+  @param join  Join object of the subquery (i.e. 'child' join).
 
-  DESCRIPTION
-    Rewrite a single-column subquery using rule-based approach. The subquery
+  @details
+  Rewrite a single-column subquery using rule-based approach. The subquery
+
+     oe $cmp$ (SELECT ie FROM ... WHERE subq_where ... HAVING subq_having)
+
+  First, try to convert the subquery to scalar-result subquery in one of
+  the forms:
     
-       oe $cmp$ (SELECT ie FROM ... WHERE subq_where ... HAVING subq_having)
-    
-    First, try to convert the subquery to scalar-result subquery in one of
-    the forms:
-    
-       - oe $cmp$ (SELECT MAX(...) )  // handled by Item_singlerow_subselect
-       - oe $cmp$ <max>(SELECT ...)   // handled by Item_maxmin_subselect
+     - oe $cmp$ (SELECT MAX(...) )  // handled by Item_singlerow_subselect
+     - oe $cmp$ <max>(SELECT ...)   // handled by Item_maxmin_subselect
+
+  If that fails, check if the subquery is a single select without tables,
+  and substitute the subquery predicate with "oe $cmp$ ie".
    
-    If that fails, the subquery will be handled with class Item_in_optimizer, 
-    Inject the predicates into subquery, i.e. convert it to:
+  If that fails, the subquery predicate is wrapped into an Item_in_optimizer.
+  Later the query optimization phase chooses whether the subquery under the
+  Item_in_optimizer will be further transformed into an equivalent correlated
+  EXISTS by injecting additional predicates, or will be executed via subquery
+  materialization in its unmodified form.
 
-    - If the subquery has aggregates, GROUP BY, or HAVING, convert to
-
-       SELECT ie FROM ...  HAVING subq_having AND 
-                                   trigcond(oe $cmp$ ref_or_null_helper<ie>)
-                                   
-      the addition is wrapped into trigger only when we want to distinguish
-      between NULL and FALSE results.
-
-    - Otherwise (no aggregates/GROUP BY/HAVING) convert it to one of the
-      following:
-
-      = If we don't need to distinguish between NULL and FALSE subquery:
-        
-        SELECT 1 FROM ... WHERE (oe $cmp$ ie) AND subq_where
-
-      = If we need to distinguish between those:
-
-        SELECT 1 FROM ...
-          WHERE  subq_where AND trigcond((oe $cmp$ ie) OR (ie IS NULL))
-          HAVING trigcond(<is_not_null_test>(ie))
-
-  RETURN
-    RES_OK     Either subquery was transformed, or appopriate
-                       predicates where injected into it.
-    RES_REDUCE The subquery was reduced to non-subquery
-    RES_ERROR  Error
+  @retval RES_OK     The subquery was transformed
+  @retval RES_ERROR  Error
 */
 
 Item_subselect::trans_res
-Item_in_subselect::single_value_transformer(JOIN *join,
-					    Comp_creator *func)
+Item_in_subselect::single_value_transformer(JOIN *join)
 {
   SELECT_LEX *select_lex= join->select_lex;
   DBUG_ENTER("Item_in_subselect::single_value_transformer");
@@ -1373,7 +1424,7 @@ Item_in_subselect::single_value_transformer(JOIN *join,
   {
     if (substitution)
     {
-      // It is second (third, ...) SELECT of UNION => All is done
+      /* It is second (third, ...) SELECT of UNION => All is done */
       DBUG_RETURN(RES_OK);
     }
 
@@ -1439,6 +1490,36 @@ Item_in_subselect::single_value_transformer(JOIN *join,
     DBUG_RETURN(RES_OK);
   }
 
+  Item* join_having= join->having ? join->having : join->tmp_having;
+  if (!(join_having || select_lex->with_sum_func ||
+        select_lex->group_list.elements) &&
+      select_lex->table_list.elements == 0 &&
+      !select_lex->master_unit()->is_union())
+  {
+    Item *where_item= (Item*) select_lex->item_list.head();
+    /*
+      it is single select without tables => possible optimization
+      remove the dependence mark since the item is moved to upper
+      select and is not outer anymore.
+    */
+    where_item->walk(&Item::remove_dependence_processor, 0,
+                     (uchar *) select_lex->outer_select());
+    substitution= func->create(left_expr, where_item);
+    have_to_be_excluded= 1;
+    if (thd->lex->describe)
+    {
+      char warn_buff[MYSQL_ERRMSG_SIZE];
+      sprintf(warn_buff, ER(ER_SELECT_REDUCED), select_lex->select_number);
+      push_warning(thd, MYSQL_ERROR::WARN_LEVEL_NOTE,
+                   ER_SELECT_REDUCED, warn_buff);
+    }
+    DBUG_RETURN(RES_OK);
+  }
+
+  /*
+    Wrap the current IN predicate in an Item_in_optimizer. The actual
+    substitution in the Item tree takes place in Item_subselect::fix_fields.
+  */
   if (!substitution)
   {
     /* We're invoked for the 1st (or the only) SELECT in the subquery UNION */
@@ -1469,33 +1550,37 @@ Item_in_subselect::single_value_transformer(JOIN *join,
 			      (char *)in_left_expr_name);
 
     master_unit->uncacheable|= UNCACHEABLE_DEPENDENT;
-    //psergey: placed then removed: select_lex->uncacheable|= UNCACHEABLE_DEPENDENT;
+    // TODO: do we need to set both?
+    // select_lex->uncacheable|= UNCACHEABLE_DEPENDENT;
   }
 
-  if (!abort_on_null && left_expr->maybe_null && !pushed_cond_guards)
+  DBUG_RETURN(RES_OK);
+}
+
+
+bool Item_in_subselect::fix_having(Item *having, SELECT_LEX *select_lex)
+{
+  bool fix_res= 0;
+  if (!having->fixed)
   {
-    if (!(pushed_cond_guards= (bool*)join->thd->alloc(sizeof(bool))))
-      DBUG_RETURN(RES_ERROR);
-    pushed_cond_guards[0]= TRUE;
+    select_lex->having_fix_field= 1;
+    fix_res= having->fix_fields(thd, 0);
+    select_lex->having_fix_field= 0;
   }
-
-  /*
-    If this IN predicate can be computed via materialization, do not
-    perform the IN -> EXISTS transformation.
-  */
-  if (exec_method == MATERIALIZATION)
-    DBUG_RETURN(RES_OK);
-
-  /* Perform the IN=>EXISTS transformation. */
-  DBUG_RETURN(single_value_in_to_exists_transformer(join, func));
+  return fix_res;
 }
 
 
 /**
-  Transofrm an IN predicate into EXISTS via predicate injection.
+  Create the predicates needed to transform a single-column IN/ALL/ANY
+  subselect into a correlated EXISTS via predicate injection.
 
-  @details The transformation injects additional predicates into the subquery
-  (and makes the subquery correlated) as follows.
+  @param join[in]  Join object of the subquery (i.e. 'child' join).
+  @param where_item[out]   the in-to-exists addition to the where clause
+  @param having_item[out]  the in-to-exists addition to the having clause
+
+  @details
+  The correlated predicates are created as follows:
 
   - If the subquery has aggregates, GROUP BY, or HAVING, convert to
 
@@ -1510,34 +1595,38 @@ Item_in_subselect::single_value_transformer(JOIN *join,
 
     = If we don't need to distinguish between NULL and FALSE subquery:
         
-      SELECT 1 FROM ... WHERE (oe $cmp$ ie) AND subq_where
+      SELECT ie FROM ... WHERE subq_where AND (oe $cmp$ ie)
 
     = If we need to distinguish between those:
 
-      SELECT 1 FROM ...
+      SELECT ie FROM ...
         WHERE  subq_where AND trigcond((oe $cmp$ ie) OR (ie IS NULL))
         HAVING trigcond(<is_not_null_test>(ie))
 
-    @param join  Join object of the subquery (i.e. 'child' join).
-    @param func  Subquery comparison creator
-
-    @retval RES_OK     Either subquery was transformed, or appopriate
-                       predicates where injected into it.
-    @retval RES_REDUCE The subquery was reduced to non-subquery
-    @retval RES_ERROR  Error
+  @retval RES_OK     If the new conditions were created successfully
+  @retval RES_ERROR  Error
 */
 
 Item_subselect::trans_res
-Item_in_subselect::single_value_in_to_exists_transformer(JOIN * join, Comp_creator *func)
+Item_in_subselect::create_single_in_to_exists_cond(JOIN * join,
+                                                   Item **where_item,
+                                                   Item **having_item)
 {
   SELECT_LEX *select_lex= join->select_lex;
-  DBUG_ENTER("Item_in_subselect::single_value_in_to_exists_transformer");
+  /*
+    The non-transformed HAVING clause of 'join' may be stored in two ways
+    during JOIN::optimize: this->tmp_having= this->having; this->having= 0;
+  */
+  Item* join_having= join->having ? join->having : join->tmp_having;
 
-  select_lex->uncacheable|= UNCACHEABLE_DEPENDENT;
-  if (join->having || select_lex->with_sum_func ||
+  DBUG_ENTER("Item_in_subselect::create_single_in_to_exists_cond");
+
+  *where_item= NULL;
+  *having_item= NULL;
+
+  if (join_having || select_lex->with_sum_func ||
       select_lex->group_list.elements)
   {
-    bool tmp;
     Item *item= func->create(expr,
                              new Item_ref_null_helper(&select_lex->context,
                                                       this,
@@ -1553,24 +1642,12 @@ Item_in_subselect::single_value_in_to_exists_transformer(JOIN * join, Comp_creat
       */
       item= new Item_func_trig_cond(item, get_cond_guard(0));
     }
-    
-    /*
-      AND and comparison functions can't be changed during fix_fields()
-      we can assign select_lex->having here, and pass 0 as last
-      argument (reference) to fix_fields()
-    */
-    select_lex->having= join->having= and_items(join->having, item);
-    if (join->having == item)
-      item->name= (char*)in_having_cond;
-    select_lex->having_fix_field= 1;
-    /*
-      we do not check join->having->fixed, because Item_and (from and_items)
-      or comparison function (from func->create) can't be fixed after creation
-    */
-    tmp= join->having->fix_fields(thd, 0);
-    select_lex->having_fix_field= 0;
-    if (tmp)
+
+    if (!join_having)
+      item->name= (char*) in_having_cond;
+    if (fix_having(item, select_lex))
       DBUG_RETURN(RES_ERROR);
+    *having_item= item;
   }
   else
   {
@@ -1578,13 +1655,8 @@ Item_in_subselect::single_value_in_to_exists_transformer(JOIN * join, Comp_creat
 
     if (select_lex->table_list.elements)
     {
-      bool tmp;
-      Item *having= item, *orig_item= item;
-      select_lex->item_list.empty();
-      select_lex->item_list.push_back(new Item_int("Not_used",
-                                                   (longlong) 1,
-                                                   MY_INT64_NUM_DECIMAL_DIGITS));
-      select_lex->ref_pointer_array[0]= select_lex->item_list.head();
+      Item *having= item;
+      Item *orig_item= item;
        
       item= func->create(expr, item);
       if (!abort_on_null && orig_item->maybe_null)
@@ -1596,23 +1668,11 @@ Item_in_subselect::single_value_in_to_exists_transformer(JOIN * join, Comp_creat
                                                 get_cond_guard(0))))
             DBUG_RETURN(RES_ERROR);
         }
-	/*
-	  Item_is_not_null_test can't be changed during fix_fields()
-	  we can assign select_lex->having here, and pass 0 as last
-	  argument (reference) to fix_fields()
-	*/
-        having->name= (char*)in_having_cond;
-	select_lex->having= join->having= having;
-	select_lex->having_fix_field= 1;
-        /*
-          we do not check join->having->fixed, because Item_and (from
-          and_items) or comparison function (from func->create) can't be
-          fixed after creation
-        */
-	tmp= join->having->fix_fields(thd, 0);
-        select_lex->having_fix_field= 0;
-        if (tmp)
-	  DBUG_RETURN(RES_ERROR);
+        having->name= (char*) in_having_cond;
+        if (fix_having(having, select_lex))
+          DBUG_RETURN(RES_ERROR);
+        *having_item= having;
+
 	item= new Item_cond_or(item,
 			       new Item_func_isnull(orig_item));
       }
@@ -1625,37 +1685,21 @@ Item_in_subselect::single_value_in_to_exists_transformer(JOIN * join, Comp_creat
         if (!(item= new Item_func_trig_cond(item, get_cond_guard(0))))
           DBUG_RETURN(RES_ERROR);
       }
+
       /*
         TODO: figure out why the following is done here in 
         single_value_transformer but there is no corresponding action in
         row_value_transformer?
       */
-      item->name= (char *)in_additional_cond;
-
-      /*
-	AND can't be changed during fix_fields()
-	we can assign select_lex->having here, and pass 0 as last
-	argument (reference) to fix_fields()
-      */
-      select_lex->where= join->conds= and_items(join->conds, item);
-      select_lex->where->top_level_item();
-      /*
-        we do not check join->conds->fixed, because Item_and can't be fixed
-        after creation
-      */
-      if (join->conds->fix_fields(thd, 0))
-	DBUG_RETURN(RES_ERROR);
+      item->name= (char *) in_additional_cond;
+      if (!item->fixed && item->fix_fields(thd, 0))
+        DBUG_RETURN(RES_ERROR);
+      *where_item= item;
     }
     else
     {
-      bool tmp;
       if (select_lex->master_unit()->is_union())
       {
-	/*
-	  comparison functions can't be changed during fix_fields()
-	  we can assign select_lex->having here, and pass 0 as last
-	  argument (reference) to fix_fields()
-	*/
         Item *new_having=
           func->create(expr,
                        new Item_ref_null_helper(&select_lex->context, this,
@@ -1668,39 +1712,14 @@ Item_in_subselect::single_value_in_to_exists_transformer(JOIN * join, Comp_creat
                                                     get_cond_guard(0))))
             DBUG_RETURN(RES_ERROR);
         }
-        new_having->name= (char*)in_having_cond;
-	select_lex->having= join->having= new_having;
-	select_lex->having_fix_field= 1;
-        
-        /*
-          we do not check join->having->fixed, because comparison function
-          (from func->create) can't be fixed after creation
-        */
-	tmp= join->having->fix_fields(thd, 0);
-        select_lex->having_fix_field= 0;
-        if (tmp)
-	  DBUG_RETURN(RES_ERROR);
+
+        new_having->name= (char*) in_having_cond;
+        if (fix_having(new_having, select_lex))
+          DBUG_RETURN(RES_ERROR);
+        *having_item= new_having;
       }
       else
-      {
-	// it is single select without tables => possible optimization
-        // remove the dependence mark since the item is moved to upper
-        // select and is not outer anymore.
-        item->walk(&Item::remove_dependence_processor, 0,
-                           (uchar *) select_lex->outer_select());
-	item= func->create(left_expr, item);
-	// fix_field of item will be done in time of substituting
-	substitution= item;
-	have_to_be_excluded= 1;
-	if (thd->lex->describe)
-	{
-	  char warn_buff[MYSQL_ERRMSG_SIZE];
-	  sprintf(warn_buff, ER(ER_SELECT_REDUCED), select_lex->select_number);
-	  push_warning(thd, MYSQL_ERROR::WARN_LEVEL_NOTE,
-		       ER_SELECT_REDUCED, warn_buff);
-	}
-	DBUG_RETURN(RES_REDUCE);
-      }
+        DBUG_ASSERT(FALSE);
     }
   }
 
@@ -1708,6 +1727,22 @@ Item_in_subselect::single_value_in_to_exists_transformer(JOIN * join, Comp_creat
 }
 
 
+/**
+  Wrap a multi-column IN/ALL/ANY subselect into an Item_in_optimizer.
+
+  @param join  Join object of the subquery (i.e. 'child' join).
+
+  @details
+  The subquery predicate is wrapped into an Item_in_optimizer. Later the query
+  optimization phase chooses whether the subquery under the Item_in_optimizer
+  will be further transformed into an equivalent correlated EXISTS by injecting
+  additional predicates, or will be executed via subquery materialization in its
+  unmodified form.
+
+  @retval RES_OK     The subquery was transformed
+  @retval RES_ERROR  Error
+*/
+
 Item_subselect::trans_res
 Item_in_subselect::row_value_transformer(JOIN *join)
 {
@@ -1747,60 +1782,51 @@ Item_in_subselect::row_value_transformer(JOIN *join)
 
     thd->lex->current_select= current;
     master_unit->uncacheable|= UNCACHEABLE_DEPENDENT;
-
-    if (!abort_on_null && left_expr->maybe_null && !pushed_cond_guards)
-    {
-      if (!(pushed_cond_guards= (bool*)join->thd->alloc(sizeof(bool) *
-                                                        left_expr->cols())))
-        DBUG_RETURN(RES_ERROR);
-      for (uint i= 0; i < cols_num; i++)
-        pushed_cond_guards[i]= TRUE;
-    }
+    // TODO: do we need to set both?
+    //select_lex->uncacheable|= UNCACHEABLE_DEPENDENT;
   }
 
-  /*
-    If this IN predicate can be computed via materialization, do not
-    perform the IN -> EXISTS transformation.
-  */
-  if (exec_method == MATERIALIZATION)
-    DBUG_RETURN(RES_OK);
-
-  /* Perform the IN=>EXISTS transformation. */
-  DBUG_RETURN(row_value_in_to_exists_transformer(join));
+  DBUG_RETURN(RES_OK);
 }
 
 
 /**
-  Tranform a (possibly non-correlated) IN subquery into a correlated EXISTS.
+  Create the predicates needed to transform a multi-column IN/ALL/ANY
+  subselect into a correlated EXISTS via predicate injection.
 
-  @todo
-  The IF-ELSE below can be refactored so that there is no duplication of the
-  statements that create the new conditions. For this we have to invert the IF
-  and the FOR statements as this:
-  for (each left operand)
-    create the equi-join condition
-    if (is_having_used || !abort_on_null)
-      create the "is null" and is_not_null_test items
-    if (is_having_used)
-      add the equi-join and the null tests to HAVING
-    else
-      add the equi-join and the "is null" to WHERE
-      add the is_not_null_test to HAVING
+  @details
+  There are two cases - either the subquery has aggregates, GROUP BY,
+  or HAVING, or not. Both cases are described inline in the code.
+
+  @param join[in]  Join object of the subquery (i.e. 'child' join).
+  @param where_item[out]   the in-to-exists addition to the where clause
+  @param having_item[out]  the in-to-exists addition to the having clause
+
+  @retval RES_OK     If the new conditions were created successfully
+  @retval RES_ERROR  Error
 */
 
 Item_subselect::trans_res
-Item_in_subselect::row_value_in_to_exists_transformer(JOIN * join)
+Item_in_subselect::create_row_in_to_exists_cond(JOIN * join,
+                                                Item **where_item,
+                                                Item **having_item)
 {
   SELECT_LEX *select_lex= join->select_lex;
-  Item *having_item= 0;
   uint cols_num= left_expr->cols();
-  bool is_having_used= (join->having || select_lex->with_sum_func ||
+  /*
+    The non-transformed HAVING clause of 'join' may be stored in two ways
+    during JOIN::optimize: this->tmp_having= this->having; this->having= 0;
+  */
+  Item* join_having= join->having ? join->having : join->tmp_having;
+  bool is_having_used= (join_having || select_lex->with_sum_func ||
                         select_lex->group_list.first ||
                         !select_lex->table_list.elements);
 
-  DBUG_ENTER("Item_in_subselect::row_value_in_to_exists_transformer");
+  DBUG_ENTER("Item_in_subselect::create_row_in_to_exists_cond");
+
+  *where_item= NULL;
+  *having_item= NULL;
 
-  select_lex->uncacheable|= UNCACHEABLE_DEPENDENT;
   if (is_having_used)
   {
     /*
@@ -1820,6 +1846,7 @@ Item_in_subselect::row_value_in_to_exists_transformer(JOIN * join)
     for (uint i= 0; i < cols_num; i++)
     {
       DBUG_ASSERT((left_expr->fixed &&
+
                   select_lex->ref_pointer_array[i]->fixed) ||
                   (select_lex->ref_pointer_array[i]->type() == REF_ITEM &&
                    ((Item_ref*)(select_lex->ref_pointer_array[i]))->ref_type() ==
@@ -1853,8 +1880,8 @@ Item_in_subselect::row_value_in_to_exists_transformer(JOIN * join)
         if (!(col_item= new Item_func_trig_cond(col_item, get_cond_guard(i))))
           DBUG_RETURN(RES_ERROR);
       }
-      having_item= and_items(having_item, col_item);
-      
+      *having_item= and_items(*having_item, col_item);
+
       Item *item_nnull_test= 
          new Item_is_not_null_test(this,
                                    new Item_ref(&select_lex->context,
@@ -1871,8 +1898,7 @@ Item_in_subselect::row_value_in_to_exists_transformer(JOIN * join)
       item_having_part2= and_items(item_having_part2, item_nnull_test);
       item_having_part2->top_level_item();
     }
-    having_item= and_items(having_item, item_having_part2);
-    having_item->top_level_item();
+    *having_item= and_items(*having_item, item_having_part2);
   }
   else
   {
@@ -1893,7 +1919,6 @@ Item_in_subselect::row_value_in_to_exists_transformer(JOIN * join)
                                (l2 = v2) and
                                (l3 = v3)
     */
-    Item *where_item= 0;
     for (uint i= 0; i < cols_num; i++)
     {
       Item *item, *item_isnull;
@@ -1951,39 +1976,26 @@ Item_in_subselect::row_value_in_to_exists_transformer(JOIN * join)
                   new Item_func_trig_cond(having_col_item, get_cond_guard(i))))
             DBUG_RETURN(RES_ERROR);
         }
-        having_item= and_items(having_item, having_col_item);
+        *having_item= and_items(*having_item, having_col_item);
       }
-      where_item= and_items(where_item, item);
+      *where_item= and_items(*where_item, item);
     }
-    /*
-      AND can't be changed during fix_fields()
-      we can assign select_lex->where here, and pass 0 as last
-      argument (reference) to fix_fields()
-    */
-    select_lex->where= join->conds= and_items(join->conds, where_item);
-    select_lex->where->top_level_item();
-    if (join->conds->fix_fields(thd, 0))
-      DBUG_RETURN(RES_ERROR);
   }
-  if (having_item)
+
+  if (*where_item)
   {
-    bool res;
-    select_lex->having= join->having= and_items(join->having, having_item);
-    if (having_item == select_lex->having)
-      having_item->name= (char*)in_having_cond;
-    select_lex->having->top_level_item();
-    /*
-      AND can't be changed during fix_fields()
-      we can assign select_lex->having here, and pass 0 as last
-      argument (reference) to fix_fields()
-    */
-    select_lex->having_fix_field= 1;
-    res= join->having->fix_fields(thd, 0);
-    select_lex->having_fix_field= 0;
-    if (res)
-    {
+    if (!(*where_item)->fixed && (*where_item)->fix_fields(thd, 0))
       DBUG_RETURN(RES_ERROR);
-    }
+    (*where_item)->top_level_item();
+  }
+
+  if (*having_item)
+  {
+    if (!join_having)
+      (*having_item)->name= (char*) in_having_cond;
+    if (fix_having(*having_item, select_lex))
+      DBUG_RETURN(RES_ERROR);
+    (*having_item)->top_level_item();
   }
 
   DBUG_RETURN(RES_OK);
@@ -1993,7 +2005,89 @@ Item_in_subselect::row_value_in_to_exists_transformer(JOIN * join)
 Item_subselect::trans_res
 Item_in_subselect::select_transformer(JOIN *join)
 {
-  return select_in_like_transformer(join, &eq_creator);
+  return select_in_like_transformer(join);
+}
+
+
+/**
+  Create the predicates needed to transform an IN/ALL/ANY subselect into a
+  correlated EXISTS via predicate injection.
+
+  @param join_arg  Join object of the subquery.
+
+  @retval FALSE  ok
+  @retval TRUE   error
+*/
+
+bool Item_in_subselect::create_in_to_exists_cond(JOIN *join_arg)
+{
+  Item_subselect::trans_res res;
+
+  DBUG_ASSERT(engine->engine_type() == subselect_engine::SINGLE_SELECT_ENGINE ||
+              engine->engine_type() == subselect_engine::UNION_ENGINE);
+  /*
+    TODO: the call to init_cond_guards allocates and initializes an
+    array of booleans that may not be used later because we may choose
+    materialization.
+    The two calls below to create_XYZ_cond depend on this boolean array.
+    If the dependency is removed, the call can be moved to a later phase.
+  */
+  init_cond_guards();
+  join_arg->select_lex->uncacheable|= UNCACHEABLE_DEPENDENT;
+  if (left_expr->cols() == 1)
+    res= create_single_in_to_exists_cond(join_arg,
+                                         &(join_arg->in_to_exists_where),
+                                         &(join_arg->in_to_exists_having));
+  else
+    res= create_row_in_to_exists_cond(join_arg,
+                                      &(join_arg->in_to_exists_where),
+                                      &(join_arg->in_to_exists_having));
+  return (res != RES_OK);
+}
+
+
+/**
+  Transform an IN/ALL/ANY subselect into a correlated EXISTS via injecting
+  correlated in-to-exists predicates.
+
+  @param join_arg  Join object of the subquery.
+
+  @retval FALSE  ok
+  @retval TRUE   error
+*/
+
+bool Item_in_subselect::inject_in_to_exists_cond(JOIN *join_arg)
+{
+  SELECT_LEX *select_lex= join_arg->select_lex;
+  Item *where_item= join_arg->in_to_exists_where;
+  Item *having_item= join_arg->in_to_exists_having;
+
+  DBUG_ENTER("Item_in_subselect::inject_in_to_exists_cond");
+
+  if (where_item)
+  {
+    where_item= and_items(join_arg->conds, where_item);
+    if (!where_item->fixed && where_item->fix_fields(thd, 0))
+      DBUG_RETURN(true);
+    // TIMOUR TODO: call optimize_cond() for the new where clause
+    thd->change_item_tree(&select_lex->where, where_item);
+    select_lex->where->top_level_item();
+    join_arg->conds= select_lex->where;
+  }
+
+  if (having_item)
+  {
+    Item* join_having= join_arg->having ? join_arg->having:join_arg->tmp_having;
+    having_item= and_items(join_having, having_item);
+    if (fix_having(having_item, select_lex))
+      DBUG_RETURN(true);
+    // TIMOUR TODO: call optimize_cond() for the new having clause
+    thd->change_item_tree(&select_lex->having, having_item);
+    select_lex->having->top_level_item();
+    join_arg->having= select_lex->having;
+  }
+
+  DBUG_RETURN(false);
 }
 
 
@@ -2001,25 +2095,20 @@ Item_in_subselect::select_transformer(JOIN *join)
   Prepare IN/ALL/ANY/SOME subquery transformation and call appropriate
   transformation function.
 
-    To decide which transformation procedure (scalar or row) applicable here
-    we have to call fix_fields() for left expression to be able to call
-    cols() method on it. Also this method make arena management for
-    underlying transformation methods.
-
   @param join    JOIN object of transforming subquery
-  @param func    creator of condition function of subquery
 
-  @retval
-    RES_OK      OK
-  @retval
-    RES_REDUCE  OK, and current subquery was reduced during
-    transformation
-  @retval
-    RES_ERROR   Error
+  @notes
+  To decide which transformation procedure (scalar or row) applicable here
+  we have to call fix_fields() for left expression to be able to call
+  cols() method on it. Also this method make arena management for
+  underlying transformation methods.
+
+  @retval  RES_OK      OK
+  @retval  RES_ERROR   Error
 */
 
 Item_subselect::trans_res
-Item_in_subselect::select_in_like_transformer(JOIN *join, Comp_creator *func)
+Item_in_subselect::select_in_like_transformer(JOIN *join)
 {
   Query_arena *arena, backup;
   SELECT_LEX *current= thd->lex->current_select;
@@ -2074,14 +2163,6 @@ Item_in_subselect::select_in_like_transformer(JOIN *join, Comp_creator *func)
   if (result)
     goto err;
 
-  /*
-    If we didn't choose an execution method up to this point, we choose
-    the IN=>EXISTS transformation.
-  */
-  if (exec_method == NOT_TRANSFORMED)
-    exec_method= IN_TO_EXISTS;
-  arena= thd->activate_stmt_arena_if_needed(&backup);
-
   /*
     Both transformers call fix_fields() only for Items created inside them,
     and all that items do not make permanent changes in current item arena
@@ -2089,8 +2170,9 @@ Item_in_subselect::select_in_like_transformer(JOIN *join, Comp_creator *func)
     of Item, we have to call fix_fields() for it only with original arena to
     avoid memory leack)
   */
+  arena= thd->activate_stmt_arena_if_needed(&backup);
   if (left_expr->cols() == 1)
-    res= single_value_transformer(join, func);
+    res= single_value_transformer(join);
   else
   {
     /* we do not support row operation for ALL/ANY/SOME */
@@ -2113,7 +2195,7 @@ err:
 
 void Item_in_subselect::print(String *str, enum_query_type query_type)
 {
-  if (exec_method == IN_TO_EXISTS)
+  if (in_strategy & SUBS_IN_TO_EXISTS)
     str->append(STRING_WITH_LEN("<exists>"));
   else
   {
@@ -2129,7 +2211,7 @@ bool Item_in_subselect::fix_fields(THD *thd_arg, Item **ref)
   uint outer_cols_num;
   List<Item> *inner_cols;
 
-  if (exec_method == SEMI_JOIN)
+  if (in_strategy & SUBS_SEMI_JOIN)
     return !( (*ref)= new Item_int(1));
 
   /*
@@ -2202,99 +2284,47 @@ void Item_in_subselect::update_used_tables()
   used_tables_cache |= left_expr->used_tables();
 }
 
+
 /**
-  Try to create an engine to compute the subselect via materialization,
-  and if this fails, revert to execution via the IN=>EXISTS transformation.
+  Try to create and initialize an engine to compute a subselect via
+  materialization.
 
   @details
-    The purpose of this method is to hide the implementation details
-    of this Item's execution. The method creates a new engine for
-    materialized execution, and initializes the engine.
-
-    If this initialization fails
-    - either because it wasn't possible to create the needed temporary table
-      and its index,
-    - or because of a memory allocation error,
-    then we revert back to execution via the IN=>EXISTS tranformation.
-
-    The initialization of the new engine is divided in two parts - a permanent
-    one that lives across prepared statements, and one that is repeated for each
-    execution.
+  The method creates a new engine for materialized execution, and initializes
+  the engine. The initialization may fail
+  - either because it wasn't possible to create the needed temporary table
+    and its index,
+  - or because of a memory allocation error,
 
   @returns
     @retval TRUE  memory allocation error occurred
     @retval FALSE an execution method was chosen successfully
 */
 
-bool Item_in_subselect::setup_engine()
+bool Item_in_subselect::setup_mat_engine()
 {
-  subselect_hash_sj_engine *new_engine= NULL;
-  bool res= FALSE;
+  subselect_hash_sj_engine       *mat_engine= NULL;
+  subselect_single_select_engine *select_engine;
 
-  DBUG_ENTER("Item_in_subselect::setup_engine");
+  DBUG_ENTER("Item_in_subselect::setup_mat_engine");
 
-  if (engine->engine_type() == subselect_engine::SINGLE_SELECT_ENGINE)
-  {
-    /* Create/initialize objects in permanent memory. */
-    subselect_single_select_engine *old_engine;
-    Query_arena *arena= thd->stmt_arena, backup;
+  /*
+    The select_engine (that executes transformed IN=>EXISTS subselects) is
+    pre-created at parse time, and is stored in statment memory (preserved
+    across PS executions).
+  */
+  DBUG_ASSERT(engine->engine_type() == subselect_engine::SINGLE_SELECT_ENGINE);
+  select_engine= (subselect_single_select_engine*) engine;
 
-    old_engine= (subselect_single_select_engine*) engine;
+  /* Create/initialize execution objects. */
+  if (!(mat_engine= new subselect_hash_sj_engine(thd, this, select_engine)))
+    DBUG_RETURN(TRUE);
 
-    if (arena->is_conventional())
-      arena= 0;
-    else
-      thd->set_n_backup_active_arena(arena, &backup);
+  if (mat_engine->init(&select_engine->join->fields_list))
+    DBUG_RETURN(TRUE);
 
-    if (!(new_engine= new subselect_hash_sj_engine(thd, this,
-                                                   old_engine)) ||
-        new_engine->init_permanent(unit->get_unit_column_types()))
-    {
-      Item_subselect::trans_res trans_res;
-      /*
-        If for some reason we cannot use materialization for this IN predicate,
-        delete all materialization-related objects, and apply the IN=>EXISTS
-        transformation.
-      */
-      delete new_engine;
-      new_engine= NULL;
-      exec_method= NOT_TRANSFORMED;
-      if (left_expr->cols() == 1)
-        trans_res= single_value_in_to_exists_transformer(old_engine->join,
-                                                         &eq_creator);
-      else
-        trans_res= row_value_in_to_exists_transformer(old_engine->join);
-      res= (trans_res != Item_subselect::RES_OK);
-    }
-    if (new_engine)
-      engine= new_engine;
-
-    if (arena)
-      thd->restore_active_arena(arena, &backup);
-  }
-  else
-  {
-    DBUG_ASSERT(engine->engine_type() == subselect_engine::HASH_SJ_ENGINE);
-    new_engine= (subselect_hash_sj_engine*) engine;
-  }
-
-  /* Initilizations done in runtime memory, repeated for each execution. */
-  if (new_engine)
-  {
-    /*
-      Reset the LIMIT 1 set in Item_exists_subselect::fix_length_and_dec.
-      TODO:
-      Currently we set the subquery LIMIT to infinity, and this is correct
-      because we forbid at parse time LIMIT inside IN subqueries (see
-      Item_in_subselect::test_limit). However, once we allow this, here
-      we should set the correct limit if given in the query.
-    */
-    unit->global_parameters->select_limit= NULL;
-    if ((res= new_engine->init_runtime()))
-      DBUG_RETURN(res);
-  }
-
-  DBUG_RETURN(res);
+  engine= mat_engine;
+  DBUG_RETURN(FALSE);
 }
 
 
@@ -2337,14 +2367,25 @@ bool Item_in_subselect::init_left_expr_cache()
 }
 
 
+bool Item_in_subselect::init_cond_guards()
+{
+  uint cols_num= left_expr->cols();
+  if (!abort_on_null && left_expr->maybe_null && !pushed_cond_guards)
+  {
+    if (!(pushed_cond_guards= (bool*)thd->alloc(sizeof(bool) * cols_num)))
+        return TRUE;
+    for (uint i= 0; i < cols_num; i++)
+      pushed_cond_guards[i]= TRUE;
+  }
+  return FALSE;
+}
+
+
 /*
   Callback to test if an IN predicate is expensive.
 
   @details
-    IN predicates are considered expensive only if they will be executed via
-    materialization. The return value affects the behavior of
-    make_cond_for_table() in such a way that it is unchanged when we use
-    the IN=>EXISTS transformation to compute IN.
+    The return value affects the behavior of make_cond_for_table().
 
   @retval TRUE  if the predicate is expensive
   @retval FALSE otherwise
@@ -2352,7 +2393,8 @@ bool Item_in_subselect::init_left_expr_cache()
 
 bool Item_in_subselect::is_expensive_processor(uchar *arg)
 {
-  return exec_method == MATERIALIZATION;
+  /* TIMOUR: TODO: decide on a cost basis whether it is expensive or not. */
+  return TRUE;
 }
 
 
@@ -2360,16 +2402,16 @@ Item_subselect::trans_res
 Item_allany_subselect::select_transformer(JOIN *join)
 {
   DBUG_ENTER("Item_allany_subselect::select_transformer");
-  exec_method= IN_TO_EXISTS;
+  in_strategy= SUBS_IN_TO_EXISTS;
   if (upper_item)
     upper_item->show= 1;
-  DBUG_RETURN(select_in_like_transformer(join, func));
+  DBUG_RETURN(select_in_like_transformer(join));
 }
 
 
 void Item_allany_subselect::print(String *str, enum_query_type query_type)
 {
-  if (exec_method == IN_TO_EXISTS)
+  if (in_strategy & SUBS_IN_TO_EXISTS)
     str->append(STRING_WITH_LEN("<exists>"));
   else
   {
@@ -3795,13 +3837,14 @@ bitmap_init_memroot(MY_BITMAP *map, uint n_bits, MEM_ROOT *mem_root)
   @retval FALSE otherwise
 */
 
-bool subselect_hash_sj_engine::init_permanent(List<Item> *tmp_columns)
+bool subselect_hash_sj_engine::init(List<Item> *tmp_columns)
 {
+  select_union *result_sink;
   /* Options to create_tmp_table. */
   ulonglong tmp_create_options= thd->options | TMP_TABLE_ALL_COLUMNS;
                              /* | TMP_TABLE_FORCE_MYISAM; TIMOUR: force MYISAM */
 
-  DBUG_ENTER("subselect_hash_sj_engine::init_permanent");
+  DBUG_ENTER("subselect_hash_sj_engine::init");
 
   if (bitmap_init_memroot(&non_null_key_parts, tmp_columns->elements,
                             thd->mem_root) ||
@@ -3830,15 +3873,16 @@ bool subselect_hash_sj_engine::init_permanent(List<Item> *tmp_columns)
     DBUG_RETURN(TRUE);
   }
 */
-  if (!(result= new select_materialize_with_stats))
+  if (!(result_sink= new select_materialize_with_stats))
+    DBUG_RETURN(TRUE);
+  result_sink->get_tmp_table_param()->materialized_subquery= true;
+  if (result_sink->create_result_table(thd, tmp_columns, TRUE,
+                                       tmp_create_options,
+                                       "materialized subselect", TRUE))
     DBUG_RETURN(TRUE);
 
-  if (((select_union*) result)->create_result_table(
-                         thd, tmp_columns, TRUE, tmp_create_options,
-                         "materialized subselect", TRUE))
-    DBUG_RETURN(TRUE);
-
-  tmp_table= ((select_union*) result)->table;
+  tmp_table= result_sink->table;
+  result= result_sink;
 
   /*
     If the subquery has blobs, or the total key lenght is bigger than
@@ -3875,6 +3919,17 @@ bool subselect_hash_sj_engine::init_permanent(List<Item> *tmp_columns)
       !(lookup_engine= make_unique_engine()))
     DBUG_RETURN(TRUE);
 
+  /*
+    Repeat name resolution for 'cond' since cond is not part of any
+    clause of the query, and it is not 'fixed' during JOIN::prepare.
+  */
+  if (semi_join_conds && !semi_join_conds->fixed &&
+      semi_join_conds->fix_fields(thd, (Item**)&semi_join_conds))
+    DBUG_RETURN(TRUE);
+  /* Let our engine reuse this query plan for materialization. */
+  materialize_join= materialize_engine->join;
+  materialize_join->change_result(result);
+
   DBUG_RETURN(FALSE);
 }
 
@@ -3987,35 +4042,6 @@ subselect_hash_sj_engine::make_unique_engine()
 }
 
 
-/**
-  Initialize members of the engine that need to be re-initilized at each
-  execution.
-
-  @retval TRUE  if a memory allocation error occurred
-  @retval FALSE if success
-*/
-
-bool subselect_hash_sj_engine::init_runtime()
-{
-  /*
-    Create and optimize the JOIN that will be used to materialize
-    the subquery if not yet created.
-  */
-  materialize_engine->prepare();
-  /*
-    Repeat name resolution for 'cond' since cond is not part of any
-    clause of the query, and it is not 'fixed' during JOIN::prepare.
-  */
-  if (semi_join_conds && !semi_join_conds->fixed &&
-      semi_join_conds->fix_fields(thd, (Item**)&semi_join_conds))
-    return TRUE;
-  /* Let our engine reuse this query plan for materialization. */
-  materialize_join= materialize_engine->join;
-  materialize_join->change_result(result);
-  return FALSE;
-}
-
-
 subselect_hash_sj_engine::~subselect_hash_sj_engine()
 {
   delete lookup_engine;
@@ -4025,6 +4051,16 @@ subselect_hash_sj_engine::~subselect_hash_sj_engine()
 }
 
 
+int subselect_hash_sj_engine::prepare()
+{
+  /*
+    Create and optimize the JOIN that will be used to materialize
+    the subquery if not yet created.
+  */
+  return materialize_engine->prepare();
+}
+
+
 /**
   Cleanup performed after each PS execution.
 
@@ -4042,6 +4078,12 @@ void subselect_hash_sj_engine::cleanup()
   count_null_only_columns= 0;
   strategy= UNDEFINED;
   materialize_engine->cleanup();
+  /*
+    Restore the original Item_in_subselect engine. This engine is created once
+    at parse time and stored across executions, while all other materialization
+    related engines are created and chosen for each execution.
+  */
+  ((Item_in_subselect *) item)->engine= materialize_engine;
   if (lookup_engine_type == TABLE_SCAN_ENGINE ||
       lookup_engine_type == ROWID_MERGE_ENGINE)
   {
@@ -4058,6 +4100,9 @@ void subselect_hash_sj_engine::cleanup()
   DBUG_ASSERT(lookup_engine->engine_type() == UNIQUESUBQUERY_ENGINE);
   lookup_engine->cleanup();
   result->cleanup(); /* Resets the temp table as well. */
+  DBUG_ASSERT(tmp_table);
+  free_tmp_table(thd, tmp_table);
+  tmp_table= NULL;
 }
 
 
@@ -4086,9 +4131,8 @@ int subselect_hash_sj_engine::exec()
     the subquery predicate.
   */
   thd->lex->current_select= materialize_engine->select_lex;
-  if ((res= materialize_join->optimize()))
-    goto err; /* purecov: inspected */
-  DBUG_ASSERT(!is_materialized); /* We should materialize only once. */
+  /* The subquery should be optimized, and materialized only once. */
+  DBUG_ASSERT(materialize_join->optimized && !is_materialized);
   materialize_join->exec();
   if ((res= test(materialize_join->error || thd->is_fatal_error)))
     goto err;
@@ -4112,11 +4156,10 @@ int subselect_hash_sj_engine::exec()
   tmp_table->file->info(HA_STATUS_VARIABLE);
   if (!tmp_table->file->stats.records)
   {
-    item_in->value= FALSE;
     /* The value of IN will not change during this execution. */
-    item_in->is_constant= TRUE;
+    item_in->reset();
+    item_in->make_const();
     item_in->set_first_execution();
-    /* TIMOUR: check if we need this: item_in->null_value= FALSE; */
     DBUG_RETURN(FALSE);
   }
 
diff --git a/sql/item_subselect.h b/sql/item_subselect.h
index 320c57b679f..85e0191348e 100644
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@@ -71,6 +71,13 @@ protected:
   
   bool inside_first_fix_fields;
   bool done_first_fix_fields;
+  /*
+    Set to TRUE if at optimization or execution time we determine that this
+    item's value is a constant. We need this member because it is not possible
+    to substitute 'this' with a constant item.
+  */
+  bool forced_const;
+
 public:
   /* A reference from inside subquery predicate to somewhere outside of it */
   class Ref_to_outside : public Sql_alloc
@@ -119,6 +126,12 @@ public:
   Item_subselect();
 
   virtual subs_type substype() { return UNKNOWN_SUBS; }
+  bool is_in_predicate()
+  {
+    return (substype() == Item_subselect::IN_SUBS ||
+            substype() == Item_subselect::ALL_SUBS ||
+            substype() == Item_subselect::ANY_SUBS);
+  }
 
   /*
     We need this method, because some compilers do not allow 'this'
@@ -149,12 +162,21 @@ public:
   void fix_after_pullout(st_select_lex *new_parent, Item **ref);
   void recalc_used_tables(st_select_lex *new_parent, bool after_pullout);
   virtual bool exec();
+  /*
+    If subquery optimization or execution determines that the subquery has
+    an empty result, mark the subquery predicate as a constant value.
+  */
+  void make_const()
+  { 
+    used_tables_cache= 0;
+    const_item_cache= 0;
+    forced_const= TRUE; 
+  }
   virtual void fix_length_and_dec();
   table_map used_tables() const;
   table_map not_null_tables() const { return 0; }
   bool const_item() const;
   inline table_map get_used_tables_cache() { return used_tables_cache; }
-  inline bool get_const_item_cache() { return const_item_cache; }
   Item *get_tmp_table_item(THD *thd);
   void update_used_tables();
   virtual void print(String *str, enum_query_type query_type);
@@ -181,6 +203,8 @@ public:
   enum_parsing_place place() { return parsing_place; }
   bool walk(Item_processor processor, bool walk_subquery, uchar *arg);
   bool mark_as_eliminated_processor(uchar *arg);
+  bool eliminate_subselect_processor(uchar *arg);
+  bool set_fake_select_as_master_processor(uchar *arg);
   bool enumerate_field_refs_processor(uchar *arg);
   bool check_vcol_func_processor(uchar *int_arg) 
   {
@@ -313,6 +337,18 @@ public:
 };
 
 
+/*
+  Possible methods to execute an IN predicate. These are set by the optimizer
+  based on user-set optimizer switches, semantic analysis and cost comparison.
+*/
+#define SUBS_NOT_TRANSFORMED 0 /* No execution method was chosen for this IN. */
+#define SUBS_SEMI_JOIN 1       /* IN was converted to semi-join. */
+#define SUBS_IN_TO_EXISTS 2    /* IN was converted to correlated EXISTS. */
+#define SUBS_MATERIALIZATION 4 /* Execute IN via subquery materialization. */
+/* Partial matching substrategies of MATERIALIZATION. */
+#define SUBS_PARTIAL_MATCH_ROWID_MERGE 8
+#define SUBS_PARTIAL_MATCH_TABLE_SCAN 16
+
 /**
   Representation of IN subquery predicates of the form
   "left_expr IN (SELECT ...)".
@@ -330,8 +366,6 @@ public:
 
 class Item_in_subselect :public Item_exists_subselect
 {
-public:
-  Item *left_expr;
 protected:
   /*
     Cache of the left operand of the subquery predicate. Allocated in the
@@ -339,12 +373,6 @@ protected:
   */
   List<Cached_item> *left_expr_cache;
   bool first_execution;
-  /*
-    Set to TRUE if at query execution time we determine that this item's
-    value is a constant during this execution. We need this member because
-    it is not possible to substitute 'this' with a constant item.
-  */
-  bool is_constant;
 
   /*
     expr & optimizer used in subselect rewriting to store Item for
@@ -354,10 +382,24 @@ protected:
   Item_in_optimizer *optimizer;
   bool was_null;
   bool abort_on_null;
-public:
   /* Used to trigger on/off conditions that were pushed down to subselect */
   bool *pushed_cond_guards;
-  
+  Comp_creator *func;
+
+protected:
+  bool init_cond_guards();
+  trans_res select_in_like_transformer(JOIN *join);
+  trans_res single_value_transformer(JOIN *join);
+  trans_res row_value_transformer(JOIN * join);
+  bool fix_having(Item *having, st_select_lex *select_lex);
+  trans_res create_single_in_to_exists_cond(JOIN * join,
+                                            Item **where_item,
+                                            Item **having_item);
+  trans_res create_row_in_to_exists_cond(JOIN * join,
+                                         Item **where_item,
+                                         Item **having_item);
+public:
+  Item *left_expr;
   /* Priority of this predicate in the convert-to-semi-join-nest process. */
   int sj_convert_priority;
   /*
@@ -388,14 +430,8 @@ public:
   */
   bool sjm_scan_allowed;
 
-  /* The method chosen to execute the IN predicate.  */
-  enum enum_exec_method {
-    NOT_TRANSFORMED, /* No execution method was chosen for this IN. */
-    SEMI_JOIN,   /* IN was converted to semi-join nest and should be removed. */
-    IN_TO_EXISTS, /* IN was converted to correlated EXISTS. */
-    MATERIALIZATION /* IN will be executed via subquery materialization. */
-  };
-  enum_exec_method exec_method;
+  /* A bitmap of possible execution strategies for an IN predicate. */
+  uchar in_strategy;
 
   bool *get_cond_guard(int i)
   {
@@ -413,9 +449,10 @@ public:
   Item_in_subselect(Item * left_expr, st_select_lex *select_lex);
   Item_in_subselect()
     :Item_exists_subselect(), left_expr_cache(0), first_execution(TRUE),
-    is_constant(FALSE), optimizer(0), abort_on_null(0),
-    pushed_cond_guards(NULL), exec_method(NOT_TRANSFORMED), upper_item(0)
-  {}
+    optimizer(0), abort_on_null(0),
+    pushed_cond_guards(NULL), func(NULL), in_strategy(0),
+    upper_item(0)
+    {}
   void cleanup();
   subs_type substype() { return IN_SUBS; }
   void reset() 
@@ -426,12 +463,9 @@ public:
     was_null= 0;
   }
   trans_res select_transformer(JOIN *join);
-  trans_res select_in_like_transformer(JOIN *join, Comp_creator *func);
-  trans_res single_value_transformer(JOIN *join, Comp_creator *func);
-  trans_res row_value_transformer(JOIN * join);
-  trans_res single_value_in_to_exists_transformer(JOIN * join,
-                                                  Comp_creator *func);
-  trans_res row_value_in_to_exists_transformer(JOIN * join);
+  bool create_in_to_exists_cond(JOIN *join_arg);
+  bool inject_in_to_exists_cond(JOIN *join_arg);
+
   virtual bool exec();
   longlong val_int();
   double val_real();
@@ -446,11 +480,12 @@ public:
   bool fix_fields(THD *thd, Item **ref);
   void fix_after_pullout(st_select_lex *new_parent, Item **ref);
   void update_used_tables();
-  bool setup_engine();
+  bool setup_mat_engine();
   bool init_left_expr_cache();
   /* Inform 'this' that it was computed, and contains a valid result. */
   void set_first_execution() { if (first_execution) first_execution= FALSE; }
   bool is_expensive_processor(uchar *arg);
+  bool is_expensive() { return TRUE; }
   bool expr_cache_is_needed(THD *thd);
   
   /* 
@@ -472,7 +507,6 @@ class Item_allany_subselect :public Item_in_subselect
 {
 public:
   chooser_compare_func_creator func_creator;
-  Comp_creator *func;
   bool all;
 
   Item_allany_subselect(Item * left_expr, chooser_compare_func_creator fc,
@@ -481,6 +515,7 @@ public:
   // only ALL subquery has upper not
   subs_type substype() { return all?ALL_SUBS:ANY_SUBS; }
   trans_res select_transformer(JOIN *join);
+  void create_comp_func(bool invert) { func= func_creator(invert); }
   virtual void print(String *str, enum_query_type query_type);
 };
 
@@ -821,10 +856,9 @@ public:
   }
   ~subselect_hash_sj_engine();
 
-  bool init_permanent(List<Item> *tmp_columns);
-  bool init_runtime();
+  bool init(List<Item> *tmp_columns);
   void cleanup();
-  int prepare() { return 0; } /* Override virtual function in base class. */
+  int prepare();
   int exec();
   virtual void print(String *str, enum_query_type query_type);
   uint cols()
diff --git a/sql/mysql_priv.h b/sql/mysql_priv.h
index 255e22005d3..3899323a38c 100644
--- a/sql/mysql_priv.h
+++ b/sql/mysql_priv.h
@@ -562,24 +562,29 @@ protected:
 #define OPTIMIZER_SWITCH_INDEX_MERGE_SORT_UNION 4
 #define OPTIMIZER_SWITCH_INDEX_MERGE_INTERSECT 8
 #define OPTIMIZER_SWITCH_INDEX_COND_PUSHDOWN 16
-
 #define OPTIMIZER_SWITCH_FIRSTMATCH 32
 #define OPTIMIZER_SWITCH_LOOSE_SCAN 64
 #define OPTIMIZER_SWITCH_MATERIALIZATION 128
-#define OPTIMIZER_SWITCH_SEMIJOIN 256
-#define OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE 512
-#define OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN 1024
-#define OPTIMIZER_SWITCH_SUBQUERY_CACHE (1<<11)
+#define OPTIMIZER_SWITCH_IN_TO_EXISTS 256
+#define OPTIMIZER_SWITCH_SEMIJOIN 512
+#define OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE 1024
+#define OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN  (1<<11)
+#define OPTIMIZER_SWITCH_SUBQUERY_CACHE  (1<<12)
 
 #ifdef DBUG_OFF
-#  define OPTIMIZER_SWITCH_LAST (1<<12)
-#else
-#  define OPTIMIZER_SWITCH_TABLE_ELIMINATION (1<<12)
 #  define OPTIMIZER_SWITCH_LAST (1<<13)
+#else
+#  define OPTIMIZER_SWITCH_TABLE_ELIMINATION (1<<13)
+#  define OPTIMIZER_SWITCH_LAST (1<<14)
 #endif
 
 #ifdef DBUG_OFF 
 /* The following must be kept in sync with optimizer_switch_str in mysqld.cc */
+/*
+TODO: Materialization is off by default to mimic 5.1/5.2 behavior.
+Once cost based choice between materialization and in-to-exists should be
+enabled by default, add OPTIMIZER_SWITCH_MATERIALIZATION
+*/
 #  define OPTIMIZER_SWITCH_DEFAULT (OPTIMIZER_SWITCH_INDEX_MERGE | \
                                     OPTIMIZER_SWITCH_INDEX_MERGE_UNION | \
                                     OPTIMIZER_SWITCH_INDEX_MERGE_SORT_UNION | \
@@ -587,7 +592,7 @@ protected:
                                     OPTIMIZER_SWITCH_INDEX_COND_PUSHDOWN | \
                                     OPTIMIZER_SWITCH_FIRSTMATCH | \
                                     OPTIMIZER_SWITCH_LOOSE_SCAN | \
-                                    OPTIMIZER_SWITCH_MATERIALIZATION | \
+                                    OPTIMIZER_SWITCH_IN_TO_EXISTS | \
                                     OPTIMIZER_SWITCH_SEMIJOIN | \
                                     OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE|\
                                     OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN|\
@@ -601,7 +606,7 @@ protected:
                                     OPTIMIZER_SWITCH_TABLE_ELIMINATION | \
                                     OPTIMIZER_SWITCH_FIRSTMATCH | \
                                     OPTIMIZER_SWITCH_LOOSE_SCAN | \
-                                    OPTIMIZER_SWITCH_MATERIALIZATION | \
+                                    OPTIMIZER_SWITCH_IN_TO_EXISTS | \
                                     OPTIMIZER_SWITCH_SEMIJOIN | \
                                     OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE|\
                                     OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN|\
diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index f8da9432732..b51ffbba7f5 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -341,7 +341,7 @@ static const char *optimizer_switch_names[]=
   "index_merge","index_merge_union","index_merge_sort_union",
   "index_merge_intersection",
   "index_condition_pushdown",
-  "firstmatch","loosescan","materialization", "semijoin",
+  "firstmatch","loosescan","materialization","in_to_exists","semijoin",
   "partial_match_rowid_merge",
   "partial_match_table_scan",
   "subquery_cache",
@@ -362,6 +362,7 @@ static const unsigned int optimizer_switch_names_len[]=
   sizeof("firstmatch") - 1,
   sizeof("loosescan") - 1,
   sizeof("materialization") - 1,
+  sizeof("in_to_exists") - 1,
   sizeof("semijoin") - 1,
   sizeof("partial_match_rowid_merge") - 1,
   sizeof("partial_match_table_scan") - 1,
@@ -460,7 +461,8 @@ static const char *optimizer_switch_str="index_merge=on,index_merge_union=on,"
                                         "index_condition_pushdown=on,"
                                         "firstmatch=on,"
                                         "loosescan=on,"
-                                        "materialization=on,"
+                                        "materialization=off,"
+                                        "in_to_exists=on,"
                                         "semijoin=on,"
                                         "partial_match_rowid_merge=on,"
                                         "partial_match_table_scan=on,"
@@ -7375,7 +7377,7 @@ thread is in the relay logs.",
   {"optimizer_switch", OPT_OPTIMIZER_SWITCH,
    "optimizer_switch=option=val[,option=val...], where option={index_merge, "
    "index_merge_union, index_merge_sort_union, index_merge_intersection, "
-   "index_condition_pushdown, firstmatch, loosescan, materialization, "
+   "index_condition_pushdown, firstmatch, loosescan, materialization, in_to_exists, "
    "semijoin, partial_match_rowid_merge, partial_match_table_scan, "
    "subquery_cache"
 #ifndef DBUG_OFF
diff --git a/sql/opt_subselect.cc b/sql/opt_subselect.cc
index a58313ec9fd..c7fddb7e663 100644
--- a/sql/opt_subselect.cc
+++ b/sql/opt_subselect.cc
@@ -67,6 +67,7 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
 {
   THD *thd=join->thd;
   st_select_lex *select_lex= join->select_lex;
+  st_select_lex_unit* parent_unit= select_lex->master_unit();
   DBUG_ENTER("check_and_do_in_subquery_rewrites");
   /*
     If 
@@ -84,8 +85,8 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
     TODO: for PS, make the whole block execute only on the first execution
   */
   Item_subselect *subselect;
-  if (!thd->lex->view_prepare_mode &&                  // (1)
-    (subselect= select_lex->master_unit()->item))      // (2)
+  if (!thd->lex->view_prepare_mode &&            // (1)
+      (subselect= parent_unit->item))            // (2)
   {
     Item_in_subselect *in_subs= NULL;
     if (subselect->substype() == Item_subselect::IN_SUBS)
@@ -129,6 +130,15 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
       if (failure)
         DBUG_RETURN(-1); /* purecov: deadcode */
     }
+    if (select_lex == parent_unit->fake_select_lex)
+    {
+      /*
+        The join and its select_lex object represent the 'fake' select used
+        to compute the result of a UNION.
+      */
+      DBUG_RETURN(0);
+    }
+
     DBUG_PRINT("info", ("Checking if subq can be converted to semi-join"));
     /*
       Check if we're in subquery that is a candidate for flattening into a
@@ -154,8 +164,8 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
         !join->having && !select_lex->with_sum_func &&                // 4
         thd->thd_marker.emb_on_expr_nest &&                           // 5
         select_lex->outer_select()->join &&                           // 6
-        select_lex->master_unit()->first_select()->leaf_tables &&     // 7
-        in_subs->exec_method == Item_in_subselect::NOT_TRANSFORMED && // 8
+        parent_unit->first_select()->leaf_tables &&                   // 7
+        !in_subs->in_strategy &&                                      // 8
         select_lex->outer_select()->leaf_tables &&                    // 9
         !((join->select_options |                                     // 10
            select_lex->outer_select()->join->select_options)          // 10
@@ -175,63 +185,82 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
     else
     {
       DBUG_PRINT("info", ("Subquery can't be converted to semi-join"));
-      /*
-        Check if the subquery predicate can be executed via materialization.
-        The required conditions are:
-        1. Subquery predicate is an IN/=ANY subq predicate
-        2. Subquery is a single SELECT (not a UNION)
-        3. Subquery is not a table-less query. In this case there is no
-           point in materializing.
-          3A The upper query is not a table-less SELECT ... FROM DUAL. We
+      /* Test if the user has set a legal combination of optimizer switches. */
+      if (!optimizer_flag(thd, OPTIMIZER_SWITCH_IN_TO_EXISTS) &&
+          !optimizer_flag(thd, OPTIMIZER_SWITCH_MATERIALIZATION))
+        my_error(ER_ILLEGAL_SUBQUERY_OPTIMIZER_SWITCHES, MYF(0));
+
+      if (in_subs)
+      {
+        /* Subquery predicate is an IN/=ANY predicate. */
+        if (optimizer_flag(thd, OPTIMIZER_SWITCH_IN_TO_EXISTS))
+          in_subs->in_strategy|= SUBS_IN_TO_EXISTS;
+        if (optimizer_flag(thd, OPTIMIZER_SWITCH_MATERIALIZATION))
+          in_subs->in_strategy|= SUBS_MATERIALIZATION;
+
+        /*
+          Check if the subquery predicate can be executed via materialization.
+          The required conditions are:
+          1. Subquery is a single SELECT (not a UNION)
+          2. Subquery is not a table-less query. In this case there is no
+             point in materializing.
+          2A The upper query is not a table-less SELECT ... FROM DUAL. We
              can't do materialization for SELECT .. FROM DUAL because it
              does not call setup_subquery_materialization(). We could make 
              SELECT ... FROM DUAL call that function but that doesn't seem
              to be the case that is worth handling.
-        4. Either the subquery predicate is a top-level predicate, or at
-           least one partial match strategy is enabled. If no partial match
-           strategy is enabled, then materialization cannot be used for
-           non-top-level queries because it cannot handle NULLs correctly.
-        5. Subquery is non-correlated
-           TODO:
-           This is an overly restrictive condition. It can be extended to:
-           (Subquery is non-correlated ||
-            Subquery is correlated to any query outer to IN predicate ||
-            (Subquery is correlated to the immediate outer query &&
-             Subquery !contains {GROUP BY, ORDER BY [LIMIT],
-             aggregate functions}) && subquery predicate is not under "NOT IN"))
-        6. No execution method was already chosen (by a prepared statement).
+          3. Either the subquery predicate is a top-level predicate, or at
+             least one partial match strategy is enabled. If no partial match
+             strategy is enabled, then materialization cannot be used for
+             non-top-level queries because it cannot handle NULLs correctly.
+          4. Subquery is non-correlated
+             TODO:
+             This is an overly restrictive condition. It can be extended to:
+             (Subquery is non-correlated ||
+              Subquery is correlated to any query outer to IN predicate ||
+              (Subquery is correlated to the immediate outer query &&
+               Subquery !contains {GROUP BY, ORDER BY [LIMIT],
+               aggregate functions}) && subquery predicate is not under "NOT IN"))
 
-        (*) The subquery must be part of a SELECT statement. The current
-             condition also excludes multi-table update statements.
+          (*) The subquery must be part of a SELECT statement. The current
+               condition also excludes multi-table update statements.
+        */
+        if (!(in_subs->in_strategy & SUBS_MATERIALIZATION && 
+              !select_lex->is_part_of_union() &&                            // 1
+              parent_unit->first_select()->leaf_tables &&                   // 2
+              thd->lex->sql_command == SQLCOM_SELECT &&                     // *
+              select_lex->outer_select()->leaf_tables &&                    // 2A
+              subquery_types_allow_materialization(in_subs) &&
+              // psergey-todo: duplicated_subselect_card_check: where it's done?
+              (in_subs->is_top_level_item() ||                               //3
+               optimizer_flag(thd,
+                              OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE) || //3
+               optimizer_flag(thd,
+                              OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN)) && //3
+              !in_subs->is_correlated))                                      //4
+        {
+          /* Materialization is not possible based on syntactic properties. */
+          in_subs->in_strategy&= ~SUBS_MATERIALIZATION;
+        }
 
-        Determine whether we will perform subquery materialization before
-        calling the IN=>EXISTS transformation, so that we know whether to
-        perform the whole transformation or only that part of it which wraps
-        Item_in_subselect in an Item_in_optimizer.
-      */
-      if (optimizer_flag(thd, OPTIMIZER_SWITCH_MATERIALIZATION)  && 
-          in_subs  &&                                                   // 1
-          !select_lex->is_part_of_union() &&                            // 2
-          select_lex->master_unit()->first_select()->leaf_tables &&     // 3
-          thd->lex->sql_command == SQLCOM_SELECT &&                     // *
-          select_lex->outer_select()->leaf_tables &&                    // 3A
-          subquery_types_allow_materialization(in_subs) &&
-          // psergey-todo: duplicated_subselect_card_check: where it's done?
-          (in_subs->is_top_level_item() ||
-           optimizer_flag(thd, OPTIMIZER_SWITCH_PARTIAL_MATCH_ROWID_MERGE) ||
-           optimizer_flag(thd, OPTIMIZER_SWITCH_PARTIAL_MATCH_TABLE_SCAN)) &&//4
-          !in_subs->is_correlated &&                                  // 5
-          in_subs->exec_method == Item_in_subselect::NOT_TRANSFORMED) // 6
-      {
-          in_subs->exec_method= Item_in_subselect::MATERIALIZATION;
+        if (!in_subs->in_strategy)
+        {
+          /*
+            If neither materialization is possible, nor the user chose
+            IN-TO-EXISTS, choose IN-TO-EXISTS as the only universal strategy.
+          */
+          in_subs->in_strategy|= SUBS_IN_TO_EXISTS;
+        }
       }
 
+      /*
+        Transform each subquery predicate according to its overloaded
+        transformer.
+      */
       Item_subselect::trans_res trans_res;
       if ((trans_res= subselect->select_transformer(join)) !=
           Item_subselect::RES_OK)
-      {
         DBUG_RETURN((trans_res == Item_subselect::RES_ERROR));
-      }
     }
   }
   DBUG_RETURN(0);
@@ -509,6 +538,15 @@ skip_conversion:
                                      FALSE))
         DBUG_RETURN(TRUE);
     }
+    /*
+      Revert to the IN->EXISTS strategy in the rare case when the subquery could
+      not be flattened.
+      TODO: This is a limitation done for simplicity. Such subqueries could also
+      be executed via materialization. In order to determine this, we should
+      re-run the test for materialization that was done in
+      check_and_do_in_subquery_rewrites.
+    */
+    (*in_subq)->in_strategy= SUBS_IN_TO_EXISTS;
   }
 
   if (arena)
@@ -769,8 +807,7 @@ static bool convert_subq_to_sj(JOIN *parent_join, Item_in_subselect *subq_pred)
   /* 3. Remove the original subquery predicate from the WHERE/ON */
 
   // The subqueries were replaced for Item_int(1) earlier
-  subq_pred->exec_method=
-    Item_in_subselect::SEMI_JOIN;         // for subsequent executions
+  subq_pred->in_strategy= SUBS_SEMI_JOIN;         // for subsequent executions
   /*TODO: also reset the 'with_subselect' there. */
 
   /* n. Adjust the parent_join->tables counter */
@@ -1167,8 +1204,8 @@ bool optimize_semijoin_nests(JOIN *join, table_map all_table_map)
         sjm->tables= n_tables;
         sjm->is_used= FALSE;
         double subjoin_out_rows, subjoin_read_time;
-        get_partial_join_cost(join, n_tables,
-                              &subjoin_read_time, &subjoin_out_rows);
+        join->get_partial_join_cost(n_tables + join->const_tables,
+                                    &subjoin_read_time, &subjoin_out_rows);
 
         sjm->materialization_cost.convert_from_cost(subjoin_read_time);
         sjm->rows= subjoin_out_rows;
@@ -3362,9 +3399,23 @@ int rewrite_to_index_subquery_engine(JOIN *join)
   JOIN_TAB* join_tab=join->join_tab;
   SELECT_LEX_UNIT *unit= join->unit;
   DBUG_ENTER("rewrite_to_index_subquery_engine");
+
   /*
     is this simple IN subquery?
   */
+  /* TODO: In order to use these more efficient subquery engines in more cases,
+     the following problems need to be solved:
+     - the code that removes GROUP BY (group_list), also adds an ORDER BY
+       (order), thus GROUP BY queries (almost?) never pass through this branch.
+       Solution: remove the test below '!join->order', because we remove the
+       ORDER clase for subqueries anyway.
+     - in order to set a more efficient engine, the optimizer needs to both
+       decide to remove GROUP BY, *and* select one of the JT_[EQ_]REF[_OR_NULL]
+       access methods, *and* loose scan should be more expensive or
+       inapliccable. When is that possible?
+     - Consider expanding the applicability of this rewrite for loose scan
+       for group by queries.
+  */
   if (!join->group_list && !join->order &&
       join->unit->item && 
       join->unit->item->substype() == Item_subselect::IN_SUBS &&
@@ -3505,3 +3556,332 @@ static void remove_subq_pushed_predicates(JOIN *join, Item **where)
 }
 
 
+/**
+  Optimize all subqueries of a query that have were flattened into a semijoin.
+
+  @details
+  Optimize all immediate children subqueries of a query.
+
+  This phase must be called after substitute_for_best_equal_field() because
+  that function may replace items with other items from a multiple equality,
+  and we need to reference the correct items in the index access method of the
+  IN predicate.
+
+  @return Operation status
+  @retval FALSE     success.
+  @retval TRUE      error occurred.
+*/
+
+bool JOIN::optimize_unflattened_subqueries()
+{
+  return select_lex->optimize_unflattened_subqueries();
+}
+
+
+/**
+  Choose an optimal strategy to execute an IN/ALL/ANY subquery predicate
+  based on cost.
+
+  @param join_tables  the set of tables joined in the subquery
+
+  @notes
+  The method chooses between the materialization and IN=>EXISTS rewrite
+  strategies for the execution of a non-flattened subquery IN predicate.
+  The cost-based decision is made as follows:
+
+  1. compute materialize_strategy_cost based on the unmodified subquery
+  2. reoptimize the subquery taking into account the IN-EXISTS predicates
+  3. compute in_exists_strategy_cost based on the reoptimized plan
+  4. compare and set the cheaper strategy
+     if (materialize_strategy_cost >= in_exists_strategy_cost)
+       in_strategy = MATERIALIZATION
+     else
+       in_strategy = IN_TO_EXISTS
+  5. if in_strategy = MATERIALIZATION and it is not possible to initialize it
+       revert to IN_TO_EXISTS
+  6. if (in_strategy == MATERIALIZATION)
+       revert the subquery plan to the original one before reoptimizing
+     else
+       inject the IN=>EXISTS predicates into the new EXISTS subquery plan
+
+  The implementation itself is a bit more complicated because it takes into
+  account two more factors:
+  - whether the user allowed both strategies through an optimizer_switch, and
+  - if materialization was the cheaper strategy, whether it can be executed
+    or not.
+
+  @retval FALSE     success.
+  @retval TRUE      error occurred.
+*/
+
+bool JOIN::choose_subquery_plan(table_map join_tables)
+{  /* The original QEP of the subquery. */
+  DYNAMIC_ARRAY save_keyuse; /* Copy of the JOIN::keyuse array. */
+  POSITION save_best_positions[MAX_TABLES+1]; /* Copy of JOIN::best_positions */
+  /* Copies of the JOIN_TAB::keyuse pointers for each JOIN_TAB. */
+  KEYUSE *save_join_tab_keyuse[MAX_TABLES];
+  /* Copies of JOIN_TAB::checked_keys for each JOIN_TAB. */
+  key_map save_join_tab_checked_keys[MAX_TABLES];
+  enum_reopt_result reopt_result= REOPT_NONE;
+  Item_in_subselect *in_subs;
+
+  if (select_lex->master_unit()->item &&
+      select_lex->master_unit()->item->is_in_predicate())
+  {
+    in_subs= (Item_in_subselect*) select_lex->master_unit()->item;
+    if (in_subs->create_in_to_exists_cond(this))
+      return true;
+  }
+  else
+    return false;
+
+  DBUG_ASSERT(in_subs->in_strategy); /* A strategy must be chosen earlier. */
+  DBUG_ASSERT(in_to_exists_where || in_to_exists_having);
+  DBUG_ASSERT(!in_to_exists_where || in_to_exists_where->fixed);
+  DBUG_ASSERT(!in_to_exists_having || in_to_exists_having->fixed);
+
+  save_keyuse.elements= 0;
+  save_keyuse.buffer= NULL;
+
+  /*
+    Compute and compare the costs of materialization and in-exists if both
+    strategies are possible and allowed by the user (checked during the prepare
+    phase.
+  */
+  if (in_subs->in_strategy & SUBS_MATERIALIZATION &&
+      in_subs->in_strategy & SUBS_IN_TO_EXISTS)
+  {
+    JOIN *outer_join= unit->outer_select() ? unit->outer_select()->join : NULL;
+    JOIN *inner_join= this;
+    /* Cost of the outer JOIN. */
+    double outer_read_time, outer_record_count;
+    /* Cost of the unmodified subquery. */
+    double inner_read_time_1, inner_record_count_1;
+    /* Cost of the subquery with injected IN-EXISTS predicates. */
+    double inner_read_time_2, inner_record_count_2;
+    /* The cost to compute IN via materialization. */
+    double materialize_strategy_cost;
+    /* The cost of the IN->EXISTS strategy. */
+    double in_exists_strategy_cost;
+
+    if (outer_join)
+      outer_join->get_partial_join_cost(outer_join->tables,
+                                        &outer_read_time, &outer_record_count);
+    else
+    {
+      /*
+        TODO: outer_join can be NULL for DELETE statements.
+        How to compute its cost?
+      */
+      outer_read_time= 1; /* TODO */
+      outer_record_count= 1;  /* TODO */
+    }
+
+    inner_join->get_partial_join_cost(inner_join->tables,
+                                      &inner_read_time_1, &inner_record_count_1);
+
+    if (in_to_exists_where && const_tables != tables)
+    {
+      /*
+        Re-optimize and cost the subquery taking into account the IN-EXISTS
+        conditions.
+      */
+      if (save_query_plan(&save_keyuse, save_best_positions,
+                          save_join_tab_keyuse, save_join_tab_checked_keys))
+        return TRUE;
+      reopt_result= reoptimize(in_to_exists_where, join_tables);
+      if (reopt_result == REOPT_OLD_PLAN)
+        restore_query_plan(&save_keyuse, save_best_positions,
+                           save_join_tab_keyuse, save_join_tab_checked_keys);
+      else if (reopt_result == REOPT_ERROR)
+        return TRUE;
+
+      inner_join->get_partial_join_cost(inner_join->tables,
+                                        &inner_read_time_2, &inner_record_count_2);
+    }
+    else
+    {
+      /* Reoptimization would not produce any better plan. */
+      inner_read_time_2= inner_read_time_1;
+      inner_record_count_2= inner_record_count_1;
+    }
+
+    /* Compute execution costs. */
+    /*
+      1. Compute the cost of the materialization strategy.
+    */
+    double materialization_cost; /* The cost of executing the subquery and */
+                                 /* storing its result in an indexed temp table.*/
+    /* The cost of a lookup into the unique index of the materialized table. */
+    double lookup_cost;
+    double write_row_cost= 1; /* TODO: what is the real cost to write a row? */
+    materialization_cost= inner_read_time_1 +
+                          inner_record_count_1 * write_row_cost;
+    /*
+      The cost of a hash/btree lookup into a unique index of a materialized
+      subquery.
+      TIMOUR: TODO: the block of code below is exact copy/paste from
+      opt_subselect.cc:optimize_semi_join_nests() - refactor it.
+    */
+    uint rowlen= get_tmp_table_rec_length(unit->first_select()->item_list);
+    if (rowlen * inner_record_count_1 < thd->variables.max_heap_table_size)
+      lookup_cost= HEAP_TEMPTABLE_LOOKUP_COST;
+    else
+      lookup_cost= DISK_TEMPTABLE_LOOKUP_COST;
+    materialize_strategy_cost= materialization_cost +
+                               outer_record_count * lookup_cost;
+
+    /*
+      2. Compute the cost of the IN=>EXISTS strategy.
+    */
+    in_exists_strategy_cost= outer_record_count * inner_read_time_2;
+
+    /* Compare the costs and choose the cheaper strategy. */
+    if (materialize_strategy_cost >= in_exists_strategy_cost)
+      in_subs->in_strategy&= ~SUBS_MATERIALIZATION;
+    else
+      in_subs->in_strategy&= ~SUBS_IN_TO_EXISTS;
+  }
+
+  /*
+    If (1) materialization is a possible strategy based on semantic analysis
+    during the prepare phase, then if
+      (2) it is more expensive than the IN->EXISTS transformation, and
+      (3) it is not possible to create usable indexes for the materialization
+          strategy,
+      fall back to IN->EXISTS.
+    otherwise
+      use materialization.
+  */
+  if (in_subs->in_strategy & SUBS_MATERIALIZATION &&
+      in_subs->setup_mat_engine())
+  {
+    /*
+      If materialization was the cheaper or the only user-selected strategy,
+      but it is not possible to execute it due to limitations in the
+      implementation, fall back to IN-TO-EXISTS.
+    */
+    in_subs->in_strategy&= ~SUBS_MATERIALIZATION;
+    in_subs->in_strategy|= SUBS_IN_TO_EXISTS;
+  }
+
+  if (in_subs->in_strategy & SUBS_MATERIALIZATION)
+  {
+    /* Restore the original query plan used for materialization. */
+    if (reopt_result == REOPT_NEW_PLAN)
+      restore_query_plan(&save_keyuse, save_best_positions,
+                         save_join_tab_keyuse, save_join_tab_checked_keys);
+
+    /* TODO: should we set/unset this flag for both select_lex and its unit? */
+    in_subs->unit->uncacheable&= ~UNCACHEABLE_DEPENDENT;
+    select_lex->uncacheable&= ~UNCACHEABLE_DEPENDENT;
+
+    /*
+      Reset the "LIMIT 1" set in Item_exists_subselect::fix_length_and_dec.
+      TODO:
+      Currently we set the subquery LIMIT to infinity, and this is correct
+      because we forbid at parse time LIMIT inside IN subqueries (see
+      Item_in_subselect::test_limit). However, once we allow this, here
+      we should set the correct limit if given in the query.
+    */
+    in_subs->unit->global_parameters->select_limit= NULL;
+    in_subs->unit->set_limit(unit->global_parameters);
+    /*
+      Set the limit of this JOIN object as well, because normally its being
+      set in the beginning of JOIN::optimize, which was already done.
+    */
+    select_limit= in_subs->unit->select_limit_cnt;
+  }
+  else if (in_subs->in_strategy & SUBS_IN_TO_EXISTS)
+  {
+    /* Keep the new query plan with injected conditions, delete the old plan. */
+    if (reopt_result == REOPT_NEW_PLAN)
+      delete_dynamic(&save_keyuse);
+
+    if (reopt_result == REOPT_NONE && in_to_exists_where && const_tables != tables)
+    {
+      /*
+        The subquery was not reoptimized either because the user allowed only the
+        IN-EXISTS strategy, or because materialization was not possible based on
+        semantic analysis. Clenup the original plan and reoptimize.
+      */
+      for (uint i= 0; i < tables; i++)
+      {
+        join_tab[i].keyuse= NULL;
+        join_tab[i].checked_keys.clear_all();
+      }
+      if ((reopt_result= reoptimize(in_to_exists_where, join_tables)) ==
+          REOPT_ERROR)
+        return TRUE;
+    }
+
+    if (in_subs->inject_in_to_exists_cond(this))
+      return TRUE;
+  }
+  else
+    DBUG_ASSERT(FALSE);
+
+  return FALSE;
+}
+
+
+/**
+  Choose a query plan for a table-less subquery.
+
+  @notes
+
+  @retval FALSE     success.
+  @retval TRUE      error occurred.
+*/
+
+bool JOIN::choose_tableless_subquery_plan()
+{
+  DBUG_ASSERT(!tables_list || !tables);
+  if (select_lex->master_unit()->item)
+  {
+    DBUG_ASSERT(select_lex->master_unit()->item->type() ==
+                Item::SUBSELECT_ITEM);
+    Item_subselect *subs_predicate= select_lex->master_unit()->item;
+
+    /*
+      If the optimizer determined that his query has an empty result,
+      in most cases the subquery predicate is a known constant value -
+      either FALSE or NULL. The implementation of Item_subselect::reset()
+      determines which one.
+    */
+    if (zero_result_cause)
+    {
+      if (!implicit_grouping)
+      {
+        /*
+          Both group by queries and non-group by queries without aggregate
+          functions produce empty subquery result.
+        */
+        subs_predicate->reset();
+        subs_predicate->make_const();
+        return FALSE;
+      }
+
+      /* TODO:
+         A further optimization is possible when a non-group query with
+         MIN/MAX/COUNT is optimized by opt_sum_query. Then, if there are
+         only MIN/MAX functions over an empty result set, the subquery
+         result is a NULL value/row, thus the value of subs_predicate is
+         NULL.
+      */
+    }
+
+    if (subs_predicate->is_in_predicate())
+    {
+      Item_in_subselect *in_subs;
+      in_subs= (Item_in_subselect*) subs_predicate;
+      in_subs->in_strategy= SUBS_IN_TO_EXISTS;
+      if (in_subs->create_in_to_exists_cond(this) ||
+          in_subs->inject_in_to_exists_cond(this))
+        return TRUE;
+      tmp_having= having;
+    }
+  }
+  return FALSE;
+}
+
diff --git a/sql/share/errmsg.txt b/sql/share/errmsg.txt
index 54061931d5f..252c69afe6c 100644
--- a/sql/share/errmsg.txt
+++ b/sql/share/errmsg.txt
@@ -6247,3 +6247,5 @@ ER_UNKNOWN_OPTION
         eng "Unknown option '%-.64s'"
 ER_BAD_OPTION_VALUE
         eng "Incorrect value '%-.64s' for option '%-.64s'"
+ER_ILLEGAL_SUBQUERY_OPTIMIZER_SWITCHES
+        eng "At least one of the 'in_to_exists' or 'materialization' optimizer_switch flags must be 'on'."
diff --git a/sql/sql_class.cc b/sql/sql_class.cc
index cd408ac723f..ef3713977df 100644
--- a/sql/sql_class.cc
+++ b/sql/sql_class.cc
@@ -2656,6 +2656,7 @@ void Query_arena::free_items()
   for (; free_list; free_list= next)
   {
     next= free_list->next;
+    DBUG_ASSERT(free_list != next);
     free_list->delete_self();
   }
   /* Postcondition: free_list is 0 */
@@ -3092,6 +3093,7 @@ void TMP_TABLE_PARAM::init()
   table_charset= 0;
   precomputed_group_by= 0;
   bit_fields_as_long= 0;
+  materialized_subquery= 0;
   skip_create_table= 0;
   DBUG_VOID_RETURN;
 }
diff --git a/sql/sql_class.h b/sql/sql_class.h
index b3d78c4c801..a47abb3c59f 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -2926,6 +2926,8 @@ public:
   uint  convert_blob_length;
   CHARSET_INFO *table_charset;
   bool schema_table;
+  /* TRUE if the temp table is created for subquery materialization. */
+  bool materialized_subquery;
   /*
     True if GROUP BY and its aggregate functions are already computed
     by a table access method (e.g. by loose index scan). In this case
@@ -2949,8 +2951,8 @@ public:
   TMP_TABLE_PARAM()
     :copy_field(0), group_parts(0),
      group_length(0), group_null_parts(0), convert_blob_length(0),
-     schema_table(0), precomputed_group_by(0), force_copy_fields(0),
-     bit_fields_as_long(0), skip_create_table(0)
+    schema_table(0), materialized_subquery(0), precomputed_group_by(0),
+    force_copy_fields(0), bit_fields_as_long(0), skip_create_table(0)
   {}
   ~TMP_TABLE_PARAM()
   {
@@ -2983,6 +2985,7 @@ public:
   virtual bool create_result_table(THD *thd, List<Item> *column_types,
                                    bool is_distinct, ulonglong options,
                                    const char *alias, bool bit_fields_as_long);
+  TMP_TABLE_PARAM *get_tmp_table_param() { return &tmp_table_param; }
 };
 
 /* Base subselect interface class */
@@ -3046,7 +3049,7 @@ protected:
   void reset();
 
 public:
-  select_materialize_with_stats() {}
+  select_materialize_with_stats() { tmp_table_param.init(); }
   virtual bool create_result_table(THD *thd, List<Item> *column_types,
                                    bool is_distinct, ulonglong options,
                                    const char *alias, bool bit_fields_as_long);
diff --git a/sql/sql_delete.cc b/sql/sql_delete.cc
index 5564d628594..9d5f99a57ec 100644
--- a/sql/sql_delete.cc
+++ b/sql/sql_delete.cc
@@ -92,6 +92,10 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
     }
   }
 
+  /* Apply the IN=>EXISTS transformation to all subqueries and optimize them. */
+  if (select_lex->optimize_unflattened_subqueries())
+    DBUG_RETURN(TRUE);
+
   const_cond= (!conds || conds->const_item());
   safe_update=test(thd->options & OPTION_SAFE_UPDATES);
   if (safe_update && const_cond)
diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index 0a4e112671e..e498b8b4a58 100644
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@@ -1735,17 +1735,29 @@ void st_select_lex_node::fast_exclude()
   
 }
 
+
 /*
-  excluding select_lex structure (except first (first select can't be
+  Exclude a node from the tree lex structure, but leave it in the global
+  list of nodes.
+*/
+
+void st_select_lex_node::exclude_from_tree()
+{
+  if ((*prev= next))
+    next->prev= prev;
+}
+
+
+/*
+  Exclude select_lex structure (except first (first select can't be
   deleted, because it is most upper select))
 */
 void st_select_lex_node::exclude()
 {
-  //exclude from global list
+  /* exclude from global list */
   fast_exclude();
-  //exclude from other structures
-  if ((*prev= next))
-    next->prev= prev;
+  /* exclude from other structures */
+  exclude_from_tree();
   /* 
      We do not need following statements, because prev pointer of first 
      list element point to master->slave
@@ -2145,8 +2157,8 @@ void st_select_lex::print_limit(THD *thd,
                     select_limit == 1, and there should be no offset_limit.
                   */
                   (((subs_type == Item_subselect::IN_SUBS) &&
-                    ((Item_in_subselect*)item)->exec_method ==
-                    Item_in_subselect::MATERIALIZATION) ?
+                    ((Item_in_subselect*)item)->in_strategy &
+                    SUBS_MATERIALIZATION) ?
                    TRUE :
                    (select_limit->val_int() == 1LL) &&
                    offset_limit == 0));
@@ -3076,6 +3088,70 @@ bool st_select_lex::add_index_hint (THD *thd, char *str, uint length)
                                             str, length));
 }
 
+
+bool st_select_lex::optimize_unflattened_subqueries()
+{
+  for (SELECT_LEX_UNIT *un= first_inner_unit(); un; un= un->next_unit())
+  {
+    Item_subselect *subquery_predicate= un->item;
+    if (subquery_predicate)
+    {
+      for (SELECT_LEX *sl= un->first_select(); sl; sl= sl->next_select())
+      {
+        JOIN *inner_join= sl->join;
+        SELECT_LEX *save_select= un->thd->lex->current_select;
+        ulonglong save_options;
+        int res;
+        /* We need only 1 row to determine existence */
+        un->set_limit(un->global_parameters);
+        un->thd->lex->current_select= sl;
+        save_options= inner_join->select_options;
+        if (un->outer_select()->options & SELECT_DESCRIBE)
+        {
+          /* Optimize the subquery in the context of EXPLAIN. */
+          set_explain_type();
+          inner_join->select_options= options;
+        }
+        res= inner_join->optimize();
+        inner_join->select_options= save_options;
+        un->thd->lex->current_select= save_select;
+        if (res)
+          return TRUE;
+      }
+    }
+  }
+  return FALSE;
+}
+
+
+/**
+  Set the EXPLAIN type for this subquery.
+*/
+
+void st_select_lex::set_explain_type()
+{
+  SELECT_LEX *first= master_unit()->first_select();
+  /* drop UNCACHEABLE_EXPLAIN, because it is for internal usage only */
+  uint8 is_uncacheable= (uncacheable & ~UNCACHEABLE_EXPLAIN);
+
+  type= ((&master_unit()->thd->lex->select_lex == this) ?
+         (first_inner_unit() || next_select() ?
+          "PRIMARY" : "SIMPLE") :
+         ((this == first) ?
+          ((linkage == DERIVED_TABLE_TYPE) ?
+           "DERIVED" :
+           ((is_uncacheable & UNCACHEABLE_DEPENDENT) ?
+            "DEPENDENT SUBQUERY" :
+            (is_uncacheable ? "UNCACHEABLE SUBQUERY" :
+             "SUBQUERY"))) :
+          ((is_uncacheable & UNCACHEABLE_DEPENDENT) ?
+           "DEPENDENT UNION":
+           is_uncacheable ? "UNCACHEABLE UNION":
+           "UNION")));
+  options|= SELECT_DESCRIBE;
+}
+
+
 /**
   A routine used by the parser to decide whether we are specifying a full
   partitioning or if only partitions to add or to split.
@@ -3093,4 +3169,3 @@ bool st_lex::is_partition_management() const
           (alter_info.flags == ALTER_ADD_PARTITION ||
            alter_info.flags == ALTER_REORGANIZE_PARTITION));
 }
-
diff --git a/sql/sql_lex.h b/sql/sql_lex.h
index 31ca121ea66..525d7c5cf46 100644
--- a/sql/sql_lex.h
+++ b/sql/sql_lex.h
@@ -439,6 +439,7 @@ public:
   st_select_lex_node(): linkage(UNSPECIFIED_TYPE) {}
   virtual ~st_select_lex_node() {}
   inline st_select_lex_node* get_master() { return master; }
+  inline void set_master(st_select_lex_node* master_arg) { master= master_arg; }
   virtual void init_query();
   virtual void init_select();
   void include_down(st_select_lex_node *upper);
@@ -446,6 +447,7 @@ public:
   void include_standalone(st_select_lex_node *sel, st_select_lex_node **ref);
   void include_global(st_select_lex_node **plink);
   void exclude();
+  void exclude_from_tree();
 
   virtual st_select_lex_unit* master_unit()= 0;
   virtual st_select_lex* outer_select()= 0;
@@ -846,6 +848,15 @@ public:
 
   void clear_index_hints(void) { index_hints= NULL; }
   bool is_part_of_union() { return master_unit()->is_union(); }
+  /*
+    Optimize all subqueries that have not been flattened into semi-joins.
+    This functionality is a method of SELECT_LEX instead of JOIN because
+    some SQL statements as DELETE do not have a corresponding JOIN object.
+  */
+  bool optimize_unflattened_subqueries();
+  /* Set the EXPLAIN type for this subquery. */
+  void set_explain_type();
+
 private:  
   /* current index hint kind. used in filling up index_hints */
   enum index_hint_type current_index_hint_type;
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index debd1b07fe5..3544c26a5d6 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -59,9 +59,9 @@ static bool make_join_statistics(JOIN *join, TABLE_LIST *leaves, COND *conds,
 static bool update_ref_and_keys(THD *thd, DYNAMIC_ARRAY *keyuse,
                                 JOIN_TAB *join_tab,
                                 uint tables, COND *conds,
-                                COND_EQUAL *cond_equal,
                                 table_map table_map, SELECT_LEX *select_lex,
                                 st_sargable_param **sargables);
+static bool sort_and_filter_keyuse(DYNAMIC_ARRAY *keyuse);
 static int sort_keyuse(KEYUSE *a,KEYUSE *b);
 static bool create_ref_for_key(JOIN *join, JOIN_TAB *j, KEYUSE *org_keyuse,
 			       table_map used_tables);
@@ -236,8 +236,6 @@ static bool update_sum_func(Item_sum **func);
 static void select_describe(JOIN *join, bool need_tmp_table,bool need_order,
 			    bool distinct, const char *message=NullS);
 static void add_group_and_distinct_keys(JOIN *join, JOIN_TAB *join_tab);
-void get_partial_join_cost(JOIN *join, uint idx, double *read_time_arg,
-                           double *record_count_arg);
 static uint make_join_orderinfo(JOIN *join);
 static int
 join_read_record_no_init(JOIN_TAB *tab);
@@ -843,6 +841,7 @@ JOIN::optimize()
                            "Impossible HAVING" : "Impossible WHERE";
       tables= 0;
       error= 0;
+      choose_tableless_subquery_plan();
       goto setup_subq_exit;
     }
   }
@@ -887,12 +886,13 @@ JOIN::optimize()
     */
     if ((res=opt_sum_query(select_lex->leaf_tables, all_fields, conds)))
     {
-      if (res == HA_ERR_KEY_NOT_FOUND)
+      if (res == HA_ERR_KEY_NOT_FOUND || res < 0)
       {
         DBUG_PRINT("info",("No matching min/max row"));
 	zero_result_cause= "No matching min/max row";
         tables= 0;
 	error=0;
+        choose_tableless_subquery_plan();
         goto setup_subq_exit;
       }
       if (res > 1)
@@ -901,14 +901,7 @@ JOIN::optimize()
         DBUG_PRINT("error",("Error from opt_sum_query"));
         DBUG_RETURN(1);
       }
-      if (res < 0)
-      {
-        DBUG_PRINT("info",("No matching min/max row"));
-        zero_result_cause= "No matching min/max row";
-        tables= 0;
-        error=0;
-        goto setup_subq_exit;
-      }
+
       DBUG_PRINT("info",("Select tables optimized away"));
       zero_result_cause= "Select tables optimized away";
       tables_list= 0;				// All tables resolved
@@ -933,17 +926,14 @@ JOIN::optimize()
                                  QT_ORDINARY););
         conds= table_independent_conds;
       }
-      goto setup_subq_exit;
     }
   }
   if (!tables_list)
   {
     DBUG_PRINT("info",("No tables"));
     error= 0;
-    /* Create all structures needed for materialized subquery execution. */
-    if (setup_subquery_materialization())
-      DBUG_RETURN(1);
-    DBUG_RETURN(0);
+    choose_tableless_subquery_plan();
+    goto setup_subq_exit;
   }
   error= -1;					// Error is sent to client
   sort_by_table= get_sort_by_table(order, group_list, select_lex->leaf_tables);
@@ -1300,8 +1290,7 @@ JOIN::optimize()
   if (!(select_options & SELECT_DESCRIBE))
     init_ftfuncs(thd, select_lex, test(order));
 
-  /* Create all structures needed for materialized subquery execution. */
-  if (setup_subquery_materialization())
+  if (optimize_unflattened_subqueries())
     DBUG_RETURN(1);
   
   int res;
@@ -1396,6 +1385,32 @@ JOIN::optimize()
   if (join_tab->is_using_loose_index_scan())
     tmp_table_param.precomputed_group_by= TRUE;
 
+  error= 0;
+  DBUG_RETURN(0);
+
+setup_subq_exit:
+  /*
+    Even with zero matching rows, subqueries in the HAVING clause may
+    need to be evaluated if there are aggregate functions in the query.
+  */
+  if (optimize_unflattened_subqueries())
+    DBUG_RETURN(1);
+  error= 0;
+  DBUG_RETURN(0);
+}
+
+
+/**
+  Create and initialize objects neeed for the execution of a query plan.
+*/
+
+int JOIN::init_execution()
+{
+  DBUG_ENTER("JOIN::init_execution");
+
+  DBUG_ASSERT(optimized);
+  initialized= true;
+
   /* Create a tmp table if distinct or if the sort is too complicated */
   if (need_tmp)
   {
@@ -1428,7 +1443,7 @@ JOIN::optimize()
 			   select_options,
                            tmp_rows_limit,
 			   (char *) "")))
-		{
+    {
       DBUG_RETURN(1);
     }
 
@@ -1514,19 +1529,6 @@ JOIN::optimize()
       DBUG_RETURN(-1);                         /* purecov: inspected */
   }
 
-  error= 0;
-  DBUG_RETURN(0);
-
-setup_subq_exit:
-  /*
-    Even with zero matching rows, subqueries in the HAVING clause may
-    need to be evaluated if there are aggregate functions in the
-    query. If we have planned to materialize the subquery, we need to
-    set it up properly before prematurely leaving optimize().
-  */
-  if (setup_subquery_materialization())
-    DBUG_RETURN(1);
-  error= 0;
   DBUG_RETURN(0);
 }
 
@@ -1745,6 +1747,9 @@ JOIN::exec()
   int      tmp_error;
   DBUG_ENTER("JOIN::exec");
 
+  if (!initialized && init_execution())
+    DBUG_VOID_RETURN;
+
   thd_proc_info(thd, "executing");
   error= 0;
   if (procedure)
@@ -2561,51 +2566,6 @@ err:
 }
 
 
-/**
-  Setup for execution all subqueries of a query, for which the optimizer
-  chose hash semi-join.
-
-  @details Iterate over all subqueries of the query, and if they are under an
-  IN predicate, and the optimizer chose to compute it via hash semi-join:
-  - try to initialize all data structures needed for the materialized execution
-    of the IN predicate,
-  - if this fails, then perform the IN=>EXISTS transformation which was
-    previously blocked during JOIN::prepare.
-
-  This method is part of the "code generation" query processing phase.
-
-  This phase must be called after substitute_for_best_equal_field() because
-  that function may replace items with other items from a multiple equality,
-  and we need to reference the correct items in the index access method of the
-  IN predicate.
-
-  @return Operation status
-  @retval FALSE     success.
-  @retval TRUE      error occurred.
-*/
-
-bool JOIN::setup_subquery_materialization()
-{
-  for (SELECT_LEX_UNIT *un= select_lex->first_inner_unit(); un;
-       un= un->next_unit())
-  {
-    for (SELECT_LEX *sl= un->first_select(); sl; sl= sl->next_select())
-    {
-      Item_subselect *subquery_predicate= sl->master_unit()->item;
-      if (subquery_predicate &&
-          subquery_predicate->substype() == Item_subselect::IN_SUBS)
-      {
-        Item_in_subselect *in_subs= (Item_in_subselect*) subquery_predicate;
-        if (in_subs->exec_method == Item_in_subselect::MATERIALIZATION &&
-            in_subs->setup_engine())
-          return TRUE;
-      }
-    }
-  }
-  return FALSE;
-}
-
-
 /*****************************************************************************
   Create JOIN_TABS, make a guess about the table types,
   Approximate how many records will be used in each table
@@ -2830,10 +2790,14 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables_arg, COND *conds,
   }
 
   if (conds || outer_join)
+  {
     if (update_ref_and_keys(join->thd, keyuse_array, stat, join->tables,
-                            conds, join->cond_equal,
-                            ~outer_join, join->select_lex, &sargables))
+                            conds, ~outer_join, join->select_lex, &sargables))
       goto error;
+    if (keyuse_array->elements && sort_and_filter_keyuse(keyuse_array))
+      goto error;
+    DBUG_EXECUTE("opt", print_keyuse_array(keyuse_array););
+  }
 
   join->const_table_map= no_rows_const_tables;
   join->const_tables= const_count;
@@ -3136,6 +3100,9 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables_arg, COND *conds,
 	   sizeof(POSITION)*join->const_tables);
     join->best_read=1.0;
   }
+  if (join->choose_subquery_plan(all_table_map & ~join->const_table_map))
+    goto error;
+
   /* Generate an execution plan from the found optimal join order. */
   DBUG_RETURN(join->thd->killed || get_best_combination(join));
 
@@ -4086,11 +4053,10 @@ static void add_key_fields_for_nj(JOIN *join, TABLE_LIST *nested_join_table,
 
 static bool
 update_ref_and_keys(THD *thd, DYNAMIC_ARRAY *keyuse,JOIN_TAB *join_tab,
-                    uint tables, COND *cond, COND_EQUAL *cond_equal,
-                    table_map normal_tables, SELECT_LEX *select_lex,
-                    SARGABLE_PARAM **sargables)
+                    uint tables, COND *cond, table_map normal_tables,
+                    SELECT_LEX *select_lex, SARGABLE_PARAM **sargables)
 {
-  uint	and_level,i,found_eq_constant;
+  uint	and_level,i;
   KEY_FIELD *key_fields, *end, *field;
   uint sz;
   uint m= max(select_lex->max_equal_elems,1);
@@ -4186,67 +4152,76 @@ update_ref_and_keys(THD *thd, DYNAMIC_ARRAY *keyuse,JOIN_TAB *join_tab,
       return TRUE;
   }
 
-  /*
-    Sort the array of possible keys and remove the following key parts:
-    - ref if there is a keypart which is a ref and a const.
-      (e.g. if there is a key(a,b) and the clause is a=3 and b=7 and b=t2.d,
-      then we skip the key part corresponding to b=t2.d)
-    - keyparts without previous keyparts
-      (e.g. if there is a key(a,b,c) but only b < 5 (or a=2 and c < 3) is
-      used in the query, we drop the partial key parts from consideration).
-    Special treatment for ft-keys.
-  */
-  if (keyuse->elements)
-  {
-    KEYUSE key_end,*prev,*save_pos,*use;
-
-    my_qsort(keyuse->buffer,keyuse->elements,sizeof(KEYUSE),
-	  (qsort_cmp) sort_keyuse);
-
-    bzero((char*) &key_end,sizeof(key_end));    /* Add for easy testing */
-    if (insert_dynamic(keyuse,(uchar*) &key_end))
-      return TRUE;
-
-    use=save_pos=dynamic_element(keyuse,0,KEYUSE*);
-    prev= &key_end;
-    found_eq_constant=0;
-    for (i=0 ; i < keyuse->elements-1 ; i++,use++)
-    {
-      if (!use->used_tables && use->optimize != KEY_OPTIMIZE_REF_OR_NULL)
-	use->table->const_key_parts[use->key]|= use->keypart_map;
-      if (use->keypart != FT_KEYPART)
-      {
-	if (use->key == prev->key && use->table == prev->table)
-	{
-	  if (prev->keypart+1 < use->keypart ||
-	      (prev->keypart == use->keypart && found_eq_constant))
-	    continue;				/* remove */
-	}
-	else if (use->keypart != 0)		// First found must be 0
-	  continue;
-      }
-
-#ifdef HAVE_valgrind
-      /* Valgrind complains about overlapped memcpy when save_pos==use. */
-      if (save_pos != use)
-#endif
-        *save_pos= *use;
-      prev=use;
-      found_eq_constant= !use->used_tables;
-      /* Save ptr to first use */
-      if (!use->table->reginfo.join_tab->keyuse)
-	use->table->reginfo.join_tab->keyuse=save_pos;
-      use->table->reginfo.join_tab->checked_keys.set_bit(use->key);
-      save_pos++;
-    }
-    i=(uint) (save_pos-(KEYUSE*) keyuse->buffer);
-    VOID(set_dynamic(keyuse,(uchar*) &key_end,i));
-    keyuse->elements=i;
-  }
-  DBUG_EXECUTE("opt", print_keyuse_array(keyuse););
   return FALSE;
 }
 
+
+/**
+  Sort the array of possible keys and remove the following key parts:
+  - ref if there is a keypart which is a ref and a const.
+    (e.g. if there is a key(a,b) and the clause is a=3 and b=7 and b=t2.d,
+    then we skip the key part corresponding to b=t2.d)
+  - keyparts without previous keyparts
+    (e.g. if there is a key(a,b,c) but only b < 5 (or a=2 and c < 3) is
+    used in the query, we drop the partial key parts from consideration).
+  Special treatment for ft-keys.
+*/
+
+static bool sort_and_filter_keyuse(DYNAMIC_ARRAY *keyuse)
+{
+  KEYUSE key_end, *prev, *save_pos, *use;
+  uint found_eq_constant, i;
+
+  DBUG_ASSERT(keyuse->elements);
+
+  my_qsort(keyuse->buffer, keyuse->elements, sizeof(KEYUSE),
+           (qsort_cmp) sort_keyuse);
+
+  bzero((char*) &key_end, sizeof(key_end));    /* Add for easy testing */
+  if (insert_dynamic(keyuse, (uchar*) &key_end))
+    return TRUE;
+
+  use= save_pos= dynamic_element(keyuse,0,KEYUSE*);
+  prev= &key_end;
+  found_eq_constant= 0;
+
+  for (i=0 ; i < keyuse->elements-1 ; i++,use++)
+  {
+    if (!use->used_tables && use->optimize != KEY_OPTIMIZE_REF_OR_NULL)
+      use->table->const_key_parts[use->key]|= use->keypart_map;
+    if (use->keypart != FT_KEYPART)
+    {
+      if (use->key == prev->key && use->table == prev->table)
+      {
+        if (prev->keypart+1 < use->keypart ||
+            (prev->keypart == use->keypart && found_eq_constant))
+          continue;				/* remove */
+      }
+      else if (use->keypart != 0)		// First found must be 0
+        continue;
+    }
+
+#ifdef HAVE_valgrind
+    /* Valgrind complains about overlapped memcpy when save_pos==use. */
+    if (save_pos != use)
+#endif
+      *save_pos= *use;
+    prev= use;
+    found_eq_constant= !use->used_tables;
+    /* Save ptr to first use */
+    if (!use->table->reginfo.join_tab->keyuse)
+      use->table->reginfo.join_tab->keyuse=save_pos;
+    use->table->reginfo.join_tab->checked_keys.set_bit(use->key);
+    save_pos++;
+  }
+  i= (uint) (save_pos-(KEYUSE*) keyuse->buffer);
+  VOID(set_dynamic(keyuse,(uchar*) &key_end,i));
+  keyuse->elements= i;
+
+  return FALSE;
+}
+
+
 /**
   Update some values in keyuse for faster choose_plan() loop.
 */
@@ -5433,40 +5408,43 @@ greedy_search(JOIN      *join,
 }
 
 
-/*
-  Calculate a cost of given partial join order
+/**
+  Calculate a cost of given partial join order in join->positions.
  
-  SYNOPSIS
-    get_partial_join_cost()
-      join               IN    Join to use. join->positions holds the
-                               partial join order
-      idx                IN    # tables in the partial join order
-      read_time_arg      OUT   Store read time here 
-      record_count_arg   OUT   Store record count here
+  @param n_tables[in]      # tables in the partial join order after the last
+                           constant table
+  @param read_time_arg[out]    store read time here 
+  @param record_count_arg[out] store record count here
 
-  DESCRIPTION
-
-    This is needed for semi-join materialization code. The idea is that 
-    we detect sj-materialization after we've put all sj-inner tables into
-    the join prefix
+  @note
+    When used by semi-join materialization code the idea is that we
+    detect sj-materialization after we've put all sj-inner tables into
+    the join prefix.
 
       prefix-tables semi-join-inner-tables  tN
                                              ^--we're here
 
     and we'll need to get the cost of prefix-tables prefix again.
+
+    When used with non-flattened subqueries, the method computes the
+    total cost of query plan.
+
+  @returns
+    read_time_arg and record_count_arg contain the computed cost.
 */
 
-void get_partial_join_cost(JOIN *join, uint n_tables, double *read_time_arg,
-                           double *record_count_arg)
+void JOIN::get_partial_join_cost(uint n_tables,
+                                 double *read_time_arg, double *record_count_arg)
 {
   double record_count= 1;
   double read_time= 0.0;
-  for (uint i= join->const_tables; i < n_tables + join->const_tables ; i++)
+
+  for (uint i= const_tables; i < n_tables; i++)
   {
-    if (join->best_positions[i].records_read)
+    if (best_positions[i].records_read)
     {
-      record_count *= join->best_positions[i].records_read;
-      read_time += join->best_positions[i].read_time;
+      record_count *= best_positions[i].records_read;
+      read_time += best_positions[i].read_time;
     }
   }
   *read_time_arg= read_time;// + record_count / TIME_FOR_COMPARE;
@@ -11428,10 +11406,30 @@ create_tmp_table(THD *thd,TMP_TABLE_PARAM *param,List<Item> &fields,
       {
 	if (thd->is_fatal_error)
 	  goto err;				// Got OOM
-	continue;				// Some kindf of const item
+	continue;				// Some kind of const item
       }
       if (type == Item::SUM_FUNC_ITEM)
-	((Item_sum *) item)->result_field= new_field;
+      {
+        Item_sum *agg_item= (Item_sum *) item;
+        /*
+          Update the result field only if it has never been set, or if the
+          created temporary table is not to be used for subquery
+          materialization.
+
+          The reason is that for subqueries that require materialization as part
+          of their plan, we create the 'external' temporary table needed for IN
+          execution, after the 'internal' temporary table needed for grouping.
+          Since both the external and the internal temporary tables are created
+          for the same list of SELECT fields of the subquery, setting
+          'result_field' for each invocation of create_tmp_table overrides the
+           previous value of 'result_field'.
+
+          The condition below prevents the creation of the external temp table
+          to override the 'result_field' that was set for the internal temp table.
+        */
+        if (!agg_item->result_field || !param->materialized_subquery)
+          agg_item->result_field= new_field;
+      }
       tmp_from_field++;
       reclength+=new_field->pack_length();
       if (!(new_field->flags & NOT_NULL_FLAG))
@@ -18895,28 +18893,9 @@ bool mysql_explain_union(THD *thd, SELECT_LEX_UNIT *unit, select_result *result)
   bool res= 0;
   SELECT_LEX *first= unit->first_select();
 
-  for (SELECT_LEX *sl= first;
-       sl;
-       sl= sl->next_select())
-  {
-    // drop UNCACHEABLE_EXPLAIN, because it is for internal usage only
-    uint8 uncacheable= (sl->uncacheable & ~UNCACHEABLE_EXPLAIN);
-    sl->type= (((&thd->lex->select_lex)==sl)?
-	       (sl->first_inner_unit() || sl->next_select() ? 
-		"PRIMARY" : "SIMPLE"):
-	       ((sl == first)?
-		((sl->linkage == DERIVED_TABLE_TYPE) ?
-		 "DERIVED":
-		 ((uncacheable & UNCACHEABLE_DEPENDENT) ?
-		  "DEPENDENT SUBQUERY":
-		  (uncacheable?"UNCACHEABLE SUBQUERY":
-		   "SUBQUERY"))):
-		((uncacheable & UNCACHEABLE_DEPENDENT) ?
-		 "DEPENDENT UNION":
-		 uncacheable?"UNCACHEABLE UNION":
-		 "UNION")));
-    sl->options|= SELECT_DESCRIBE;
-  }
+  for (SELECT_LEX *sl= first; sl; sl= sl->next_select())
+    sl->set_explain_type();
+
   if (unit->is_union())
   {
     unit->fake_select_lex->select_number= UINT_MAX; // jost for initialization
@@ -19334,6 +19313,8 @@ bool JOIN::change_result(select_result *res)
 {
   DBUG_ENTER("JOIN::change_result");
   result= res;
+  if (tmp_join)
+    tmp_join->result= res;
   if (!procedure && (result->prepare(fields_list, select_lex->master_unit()) ||
                      result->prepare2()))
   {
@@ -19342,6 +19323,155 @@ bool JOIN::change_result(select_result *res)
   DBUG_RETURN(FALSE);
 }
 
+
+/**
+  Save a query execution plan so that the caller can revert to it if needed,
+  and reset the current query plan so that it can be reoptimized.
+
+  @param save_keyuse[out]  a KEYUSE array to save JOIN::keyuse
+  @param save_best_positions[out]  array to save JOIN::best_positions
+  @param save_join_tab_keyuse[out] array of KEYUSE pointers to save each
+                                   JOIN_TAB::keyuse pointer
+  @param save_join_tab_checked_keys[out] an array of bitmaps to save
+                                         each JOIN_TAB::checked_keys
+
+  @retval 0  OK
+  @retval 1  memory allocation error
+*/
+int JOIN::save_query_plan(DYNAMIC_ARRAY *save_keyuse,
+                          POSITION *save_best_positions,
+                          KEYUSE **save_join_tab_keyuse,
+                          key_map *save_join_tab_checked_keys)
+{
+  if (keyuse.elements)
+  {
+    DYNAMIC_ARRAY tmp_keyuse;
+    if (my_init_dynamic_array(save_keyuse, sizeof(KEYUSE), 20, 64))
+      return 1;
+    /* Swap the current and the backup keyuse arrays. */
+    tmp_keyuse= keyuse;
+    keyuse= (*save_keyuse);
+    (*save_keyuse)= tmp_keyuse;
+
+    for (uint i= 0; i < tables; i++)
+    {
+      save_join_tab_keyuse[i]= join_tab[i].keyuse;
+      join_tab[i].keyuse= NULL;
+      save_join_tab_checked_keys[i]= join_tab[i].checked_keys;
+      join_tab[i].checked_keys.clear_all();
+    }
+  }
+  memcpy((uchar*) save_best_positions, (uchar*) best_positions,
+         sizeof(POSITION) * (tables + 1));
+  memset(best_positions, 0, sizeof(POSITION) * (tables + 1));
+  return 0;
+}
+
+
+/**
+  Restore a query plan previously saved by the caller.
+
+  @param save_keyuse  a KEYUSE array to restore into JOIN::keyuse
+  @param save_best_positions  array to restore into JOIN::best_positions
+  @param save_join_tab_keyuse array of KEYUSE pointers to restore each
+                                   JOIN_TAB::keyuse pointer
+  @param save_join_tab_checked_keys an array of bitmaps to restore
+                                         each JOIN_TAB::checked_keys
+*/
+
+void JOIN::restore_query_plan(DYNAMIC_ARRAY *save_keyuse,
+                              POSITION *save_best_positions,
+                              KEYUSE **save_join_tab_keyuse,
+                              key_map *save_join_tab_checked_keys)
+{
+  if (save_keyuse->elements)
+  {
+    DYNAMIC_ARRAY tmp_keyuse;
+    tmp_keyuse= keyuse;
+    keyuse= (*save_keyuse);
+    (*save_keyuse)= tmp_keyuse;
+    delete_dynamic(save_keyuse);
+
+    for (uint i= 0; i < tables; i++)
+    {
+      join_tab[i].keyuse= save_join_tab_keyuse[i];
+      join_tab[i].checked_keys= save_join_tab_checked_keys[i];
+    }
+
+  }
+  memcpy((uchar*) best_positions, (uchar*) save_best_positions,
+         sizeof(POSITION) * (tables + 1));
+}
+
+
+/**
+  Reoptimize a query plan taking into account an additional conjunct to the
+  WHERE clause.
+
+  @param added_where  An extra conjunct to the WHERE clause to reoptimize with
+  @param join_tables  The set of tables to reoptimize
+  @param save_best_positions  The join order of the original plan to restore to
+                              if needed.
+
+  @notes
+  Given a query plan that already optimized taking into account some WHERE clause
+  'C', reoptimize this plan with a new WHERE clause 'C AND added_where'. The
+  reoptimization works as follows:
+
+  1. Call update_ref_and_keys *only* for the new conditions 'added_where'
+     that are about to be injected into the query.
+  2. Expand if necessary the original KEYUSE array JOIN::keyuse to
+     accommodate the new REF accesses computed for the 'added_where' condition.
+  3. Add the new KEYUSEs into JOIN::keyuse.
+  4. Re-sort and re-filter the JOIN::keyuse array with the newly added
+     KEYUSE elements. 
+ 
+  @retval REOPT_NEW_PLAN  there is a new plan.
+  @retval REOPT_OLD_PLAN  no new improved plan was produced, use the old one.
+  @retval REOPT_ERROR     an irrecovarable error occured during reoptimization.
+*/
+
+JOIN::enum_reopt_result JOIN::reoptimize(Item *added_where, table_map join_tables)
+{
+  DYNAMIC_ARRAY added_keyuse;
+  SARGABLE_PARAM *sargables= 0; /* Used only as a dummy parameter. */
+
+  /* Re-run the REF optimizer to take into account the new conditions. */
+  if (update_ref_and_keys(thd, &added_keyuse, join_tab, tables, added_where,
+                          ~outer_join, select_lex, &sargables))
+  {
+    delete_dynamic(&added_keyuse);
+    return REOPT_ERROR;
+  }
+
+  if (!added_keyuse.elements)
+    return REOPT_OLD_PLAN;
+
+  /* Add the new access methods to the keyuse array. */
+  if (!keyuse.buffer &&
+      my_init_dynamic_array(&keyuse, sizeof(KEYUSE), 20, 64))
+  {
+    delete_dynamic(&added_keyuse);
+    return REOPT_ERROR;
+  }
+  allocate_dynamic(&keyuse, keyuse.elements + added_keyuse.elements);
+  memcpy(keyuse.buffer + keyuse.elements * keyuse.size_of_element,
+         added_keyuse.buffer,
+         (size_t) added_keyuse.elements * added_keyuse.size_of_element);
+  keyuse.elements+= added_keyuse.elements;
+  delete_dynamic(&added_keyuse);
+
+  if (sort_and_filter_keyuse(&keyuse))
+    return REOPT_ERROR;
+  optimize_keyuse(this, &keyuse);
+
+  /* Re-run the join optimizer to compute a new query plan. */
+  if (choose_plan(this, join_tables))
+    return REOPT_ERROR;
+
+  return REOPT_NEW_PLAN;
+}
+
 /**
   @} (end of group Query_Optimizer)
 */
diff --git a/sql/sql_select.h b/sql/sql_select.h
index 885cff0163c..574e614594a 100644
--- a/sql/sql_select.h
+++ b/sql/sql_select.h
@@ -1369,8 +1369,30 @@ inline bool sj_is_materialize_strategy(uint strategy)
 
 class JOIN :public Sql_alloc
 {
+private:
   JOIN(const JOIN &rhs);                        /**< not implemented */
   JOIN& operator=(const JOIN &rhs);             /**< not implemented */
+
+protected:
+  /* Results of reoptimizing a JOIN via JOIN::reoptimize(). */
+  enum enum_reopt_result {
+    REOPT_NEW_PLAN, /* there is a new reoptimized plan */
+    REOPT_OLD_PLAN, /* no new improved plan can be found, use the old one */
+    REOPT_ERROR,    /* an irrecovarable error occured during reoptimization */
+    REOPT_NONE      /* not yet reoptimized */
+  };
+
+  /* Support for plan reoptimization with rewritten conditions. */
+  enum_reopt_result reoptimize(Item *added_where, table_map join_tables);
+  int save_query_plan(DYNAMIC_ARRAY *save_keyuse, POSITION *save_positions,
+                      KEYUSE **save_join_tab_keyuse,
+                      key_map *save_join_tab_checked_keys);
+  void restore_query_plan(DYNAMIC_ARRAY *save_keyuse, POSITION *save_positions,
+                      KEYUSE **save_join_tab_keyuse,
+                      key_map *save_join_tab_checked_keys);
+  /* Choose a subquery plan for a table-less subquery. */
+  bool choose_tableless_subquery_plan();
+
 public:
   JOIN_TAB *join_tab,**best_ref;
   JOIN_TAB **map2table;    ///< mapping between table indexes and JOIN_TABs
@@ -1581,8 +1603,15 @@ public:
   
   bool union_part; ///< this subselect is part of union 
   bool optimized; ///< flag to avoid double optimization in EXPLAIN
+  bool initialized; ///< flag to avoid double init_execution calls
 
   Array<Item_in_subselect> sj_subselects;
+  /*
+    Additional WHERE and HAVING predicates to be considered for IN=>EXISTS
+    subquery transformation of a JOIN object.
+  */
+  Item *in_to_exists_where;
+  Item *in_to_exists_having;
 
   /* Temporary tables used to weed-out semi-join duplicates */
   List<TABLE> sj_tmp_tables;
@@ -1657,6 +1686,7 @@ public:
     ref_pointer_array_size= 0;
     zero_result_cause= 0;
     optimized= 0;
+    initialized= 0;
     cond_equal= 0;
     having_equal= 0;
     group_optimized_away= 0;
@@ -1672,6 +1702,8 @@ public:
 
     no_const_tables= FALSE;
     first_select= sub_select;
+    in_to_exists_where= NULL;
+    in_to_exists_having= NULL;
   }
 
   int prepare(Item ***rref_pointer_array, TABLE_LIST *tables, uint wind_num,
@@ -1680,12 +1712,13 @@ public:
 	      SELECT_LEX_UNIT *unit);
   int optimize();
   int reinit();
+  int init_execution();
   void exec();
   int destroy();
   void restore_tmp();
   bool alloc_func_list();
   bool flatten_subqueries();
-  bool setup_subquery_materialization();
+  bool optimize_unflattened_subqueries();
   bool make_sum_func_list(List<Item> &all_fields, List<Item> &send_fields,
 			  bool before_group_by, bool recompute= FALSE);
 
@@ -1745,6 +1778,10 @@ public:
               NULL : join_tab+const_tables;
   }
   bool setup_subquery_caches();
+  bool choose_subquery_plan(table_map join_tables);
+  void get_partial_join_cost(uint n_tables,
+                             double *read_time_arg, double *record_count_arg);
+
 private:
   /**
     TRUE if the query contains an aggregate function but has no GROUP
@@ -1977,8 +2014,6 @@ inline Item * and_items(Item* cond, Item *item)
   return (cond? (new Item_cond_and(cond, item)) : item);
 }
 bool choose_plan(JOIN *join,table_map join_tables);
-void get_partial_join_cost(JOIN *join, uint n_tables, double *read_time_arg,
-                           double *record_count_arg);
 void optimize_wo_join_buffering(JOIN *join, uint first_tab, uint last_tab, 
                                 table_map last_remaining_tables, 
                                 bool first_alt, uint no_jbuf_before,
diff --git a/sql/sql_union.cc b/sql/sql_union.cc
index 33fedb67ac4..5ca2685e9a4 100644
--- a/sql/sql_union.cc
+++ b/sql/sql_union.cc
@@ -185,6 +185,8 @@ st_select_lex_unit::init_prepare_fake_select_lex(THD *thd_arg)
   {
     (*order->item)->walk(&Item::change_context_processor, 0,
                          (uchar*) &fake_select_lex->context);
+    (*order->item)->walk(&Item::set_fake_select_as_master_processor, 0,
+                         (uchar*) fake_select_lex);
   }
 }
 
@@ -270,6 +272,18 @@ bool st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
 
     can_skip_order_by= is_union_select && !(sl->braces && sl->explicit_limit);
 
+    /*
+      Remove all references from the select_lex_units to the subqueries that
+      are inside the ORDER BY clause.
+    */
+    if (can_skip_order_by)
+    {
+      for (ORDER *ord= (ORDER *)sl->order_list.first; ord; ord= ord->next)
+      {
+        (*ord->item)->walk(&Item::eliminate_subselect_processor, FALSE, NULL);
+      }
+    }
+
     saved_error= join->prepare(&sl->ref_pointer_array,
                                sl->table_list.first,
                                sl->with_wild,
diff --git a/sql/sql_update.cc b/sql/sql_update.cc
index acdf262f977..99dd032dd78 100644
--- a/sql/sql_update.cc
+++ b/sql/sql_update.cc
@@ -290,6 +290,10 @@ int mysql_update(THD *thd,
     DBUG_RETURN(1);				/* purecov: inspected */
   }
 
+  /* Apply the IN=>EXISTS transformation to all subqueries and optimize them. */
+  if (select_lex->optimize_unflattened_subqueries())
+    DBUG_RETURN(TRUE);
+
   if (select_lex->inner_refs_list.elements &&
     fix_inner_refs(thd, all_fields, select_lex, select_lex->ref_pointer_array))
     DBUG_RETURN(1);