Fix bug lp:985667, MDEV-229

Analysis: The reason for the wrong result is the interaction between constant optimization (in this case 1-row table) and subquery optimization. - First the outer query is optimized, and 'make_join_statistics' finds that table t2 has one row, reads that row, and marks the whole table as constant. This also means that all fields of t2 are constant. - Next, we optimize the subquery in the end of the outer 'make_join_statistics'. The field 'f2' is considered constant, with value '3'. The subquery predicate is rewritten as the constant TRUE. - The outer query execution detects early that the whole query result is empty and calls 'return_zero_rows'. Since the query is with implicit grouping, we have to produce one row with special values for the aggregates (depending on each aggregate function), and NULL values for all non-aggregate fields. This function calls 'no_rows_in_result' to set each aggregate function to the default value when it aggregates over an empty result, and then calls 'send_data', which in turn evaluates each Item in the SELECT list. - When evaluation reaches the subquery predicate, it executes the subquery with field 'f2' having a constant value '3', and the subquery produces the incorrect result '7'. Solution: Implement Item::no_rows_in_result for all subquery predicates. In order to make this work, it is also needed to make all val_* methods of all subquery predicates respect the Item_subselect::forced_const flag. Otherwise subqueries are executed anyways, and override the default value set by no_rows_in_result with whatever result is produced from the subquery evaluation.
2012-04-27 12:59:17 +03:00 · 2012-04-27 12:59:17 +03:00 · c04786d3e3
commit c04786d3e3
parent 76d6549972
11 changed files with 312 additions and 16 deletions
--- a/mysql-test/r/subselect.result
+++ b/mysql-test/r/subselect.result
@ -4532,7 +4532,7 @@ SELECT MAX(b), (SELECT COUNT(*) FROM st1,st2 WHERE st2.b <= t1.b)
 FROM t1 
 WHERE a = 230;
 MAX(b)	(SELECT COUNT(*) FROM st1,st2 WHERE st2.b <= t1.b)
-NULL	0
+NULL	NULL
 DROP TABLE t1, st1, st2;
 #
 # Bug #48709: Assertion failed in sql_select.cc:11782: 
@ -6004,5 +6004,46 @@ INSERT INTO t1 VALUES (1);
 SELECT a FROM t1 WHERE ( SELECT MIN(a) = 100 );
 a
 drop table t1;
+#
+# LP BUG#985667 Wrong result with subquery in SELECT clause, and constant table in 
+# main query and implicit grouping
+#
+CREATE TABLE t1 (f1 int) engine=MyISAM;
+INSERT INTO t1 VALUES (7),(8);
+CREATE TABLE t2 (f2 int, f3 varchar(1)) engine=MyISAM;
+INSERT INTO t2 VALUES (3,'f');
+EXPLAIN
+SELECT COUNT(f1), (SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	
+SELECT COUNT(f1), (SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	NULL
+EXPLAIN
+SELECT COUNT(f1), exists(SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	
+SELECT COUNT(f1), exists(SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	0
+EXPLAIN
+SELECT COUNT(f1), f2 > ALL (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT COUNT(f1), f2 > ALL (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	1
+EXPLAIN
+SELECT COUNT(f1), f2 IN (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT COUNT(f1), f2 IN (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	0
+drop table t1,t2;
 # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;
--- a/mysql-test/r/subselect_no_mat.result
+++ b/mysql-test/r/subselect_no_mat.result
@ -4534,7 +4534,7 @@ SELECT MAX(b), (SELECT COUNT(*) FROM st1,st2 WHERE st2.b <= t1.b)
 FROM t1 
 WHERE a = 230;
 MAX(b)	(SELECT COUNT(*) FROM st1,st2 WHERE st2.b <= t1.b)
-NULL	0
+NULL	NULL
 DROP TABLE t1, st1, st2;
 #
 # Bug #48709: Assertion failed in sql_select.cc:11782: 
@ -6003,6 +6003,47 @@ INSERT INTO t1 VALUES (1);
 SELECT a FROM t1 WHERE ( SELECT MIN(a) = 100 );
 a
 drop table t1;
+#
+# LP BUG#985667 Wrong result with subquery in SELECT clause, and constant table in 
+# main query and implicit grouping
+#
+CREATE TABLE t1 (f1 int) engine=MyISAM;
+INSERT INTO t1 VALUES (7),(8);
+CREATE TABLE t2 (f2 int, f3 varchar(1)) engine=MyISAM;
+INSERT INTO t2 VALUES (3,'f');
+EXPLAIN
+SELECT COUNT(f1), (SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	
+SELECT COUNT(f1), (SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	NULL
+EXPLAIN
+SELECT COUNT(f1), exists(SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	
+SELECT COUNT(f1), exists(SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	0
+EXPLAIN
+SELECT COUNT(f1), f2 > ALL (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT COUNT(f1), f2 > ALL (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	1
+EXPLAIN
+SELECT COUNT(f1), f2 IN (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT COUNT(f1), f2 IN (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	0
+drop table t1,t2;
 # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;
 set optimizer_switch=default;
--- a/mysql-test/r/subselect_no_opts.result
+++ b/mysql-test/r/subselect_no_opts.result
@ -4530,7 +4530,7 @@ SELECT MAX(b), (SELECT COUNT(*) FROM st1,st2 WHERE st2.b <= t1.b)
 FROM t1 
 WHERE a = 230;
 MAX(b)	(SELECT COUNT(*) FROM st1,st2 WHERE st2.b <= t1.b)
-NULL	0
+NULL	NULL
 DROP TABLE t1, st1, st2;
 #
 # Bug #48709: Assertion failed in sql_select.cc:11782: 
@ -5999,6 +5999,47 @@ INSERT INTO t1 VALUES (1);
 SELECT a FROM t1 WHERE ( SELECT MIN(a) = 100 );
 a
 drop table t1;
+#
+# LP BUG#985667 Wrong result with subquery in SELECT clause, and constant table in 
+# main query and implicit grouping
+#
+CREATE TABLE t1 (f1 int) engine=MyISAM;
+INSERT INTO t1 VALUES (7),(8);
+CREATE TABLE t2 (f2 int, f3 varchar(1)) engine=MyISAM;
+INSERT INTO t2 VALUES (3,'f');
+EXPLAIN
+SELECT COUNT(f1), (SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	
+SELECT COUNT(f1), (SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	NULL
+EXPLAIN
+SELECT COUNT(f1), exists(SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	
+SELECT COUNT(f1), exists(SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	0
+EXPLAIN
+SELECT COUNT(f1), f2 > ALL (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT COUNT(f1), f2 > ALL (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	1
+EXPLAIN
+SELECT COUNT(f1), f2 IN (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT COUNT(f1), f2 IN (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	0
+drop table t1,t2;
 # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;
 set @optimizer_switch_for_subselect_test=null;
--- a/mysql-test/r/subselect_no_scache.result
+++ b/mysql-test/r/subselect_no_scache.result
@ -4538,7 +4538,7 @@ SELECT MAX(b), (SELECT COUNT(*) FROM st1,st2 WHERE st2.b <= t1.b)
 FROM t1 
 WHERE a = 230;
 MAX(b)	(SELECT COUNT(*) FROM st1,st2 WHERE st2.b <= t1.b)
-NULL	0
+NULL	NULL
 DROP TABLE t1, st1, st2;
 #
 # Bug #48709: Assertion failed in sql_select.cc:11782: 
@ -6010,6 +6010,47 @@ INSERT INTO t1 VALUES (1);
 SELECT a FROM t1 WHERE ( SELECT MIN(a) = 100 );
 a
 drop table t1;
+#
+# LP BUG#985667 Wrong result with subquery in SELECT clause, and constant table in 
+# main query and implicit grouping
+#
+CREATE TABLE t1 (f1 int) engine=MyISAM;
+INSERT INTO t1 VALUES (7),(8);
+CREATE TABLE t2 (f2 int, f3 varchar(1)) engine=MyISAM;
+INSERT INTO t2 VALUES (3,'f');
+EXPLAIN
+SELECT COUNT(f1), (SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	
+SELECT COUNT(f1), (SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	NULL
+EXPLAIN
+SELECT COUNT(f1), exists(SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	
+SELECT COUNT(f1), exists(SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	0
+EXPLAIN
+SELECT COUNT(f1), f2 > ALL (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT COUNT(f1), f2 > ALL (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	1
+EXPLAIN
+SELECT COUNT(f1), f2 IN (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT COUNT(f1), f2 IN (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	0
+drop table t1,t2;
 # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;
 set optimizer_switch=default;
--- a/mysql-test/r/subselect_no_semijoin.result
+++ b/mysql-test/r/subselect_no_semijoin.result
@ -4530,7 +4530,7 @@ SELECT MAX(b), (SELECT COUNT(*) FROM st1,st2 WHERE st2.b <= t1.b)
 FROM t1 
 WHERE a = 230;
 MAX(b)	(SELECT COUNT(*) FROM st1,st2 WHERE st2.b <= t1.b)
-NULL	0
+NULL	NULL
 DROP TABLE t1, st1, st2;
 #
 # Bug #48709: Assertion failed in sql_select.cc:11782: 
@ -5999,6 +5999,47 @@ INSERT INTO t1 VALUES (1);
 SELECT a FROM t1 WHERE ( SELECT MIN(a) = 100 );
 a
 drop table t1;
+#
+# LP BUG#985667 Wrong result with subquery in SELECT clause, and constant table in 
+# main query and implicit grouping
+#
+CREATE TABLE t1 (f1 int) engine=MyISAM;
+INSERT INTO t1 VALUES (7),(8);
+CREATE TABLE t2 (f2 int, f3 varchar(1)) engine=MyISAM;
+INSERT INTO t2 VALUES (3,'f');
+EXPLAIN
+SELECT COUNT(f1), (SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	
+SELECT COUNT(f1), (SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	NULL
+EXPLAIN
+SELECT COUNT(f1), exists(SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	
+SELECT COUNT(f1), exists(SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	0
+EXPLAIN
+SELECT COUNT(f1), f2 > ALL (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT COUNT(f1), f2 > ALL (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	1
+EXPLAIN
+SELECT COUNT(f1), f2 IN (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+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
+2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+SELECT COUNT(f1), f2 IN (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+COUNT(f1)	f4
+0	0
+drop table t1,t2;
 # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;
 set @optimizer_switch_for_subselect_test=null;
--- a/mysql-test/t/subselect.test
+++ b/mysql-test/t/subselect.test
@ -5090,6 +5090,35 @@ SELECT a FROM t1 WHERE ( SELECT MIN(a) = 100 );

 drop table t1;

+--echo #
+--echo # LP BUG#985667 Wrong result with subquery in SELECT clause, and constant table in 
+--echo # main query and implicit grouping
+--echo #
+
+CREATE TABLE t1 (f1 int) engine=MyISAM;
+INSERT INTO t1 VALUES (7),(8);
+
+CREATE TABLE t2 (f2 int, f3 varchar(1)) engine=MyISAM;
+INSERT INTO t2 VALUES (3,'f');
+
+EXPLAIN
+SELECT COUNT(f1), (SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+SELECT COUNT(f1), (SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+
+EXPLAIN
+SELECT COUNT(f1), exists(SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+SELECT COUNT(f1), exists(SELECT f1 FROM t1 WHERE f2 > 0 limit 1) AS f4 FROM t2, t1 WHERE 'v'= f3;
+
+EXPLAIN
+SELECT COUNT(f1), f2 > ALL (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+SELECT COUNT(f1), f2 > ALL (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+
+EXPLAIN
+SELECT COUNT(f1), f2 IN (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+SELECT COUNT(f1), f2 IN (SELECT f1 FROM t1 WHERE f2 > 0) AS f4 FROM t2, t1 WHERE 'v'= f3;
+
+drop table t1,t2;
+

 --echo # return optimizer switch changed in the beginning of this test
 set optimizer_switch=@subselect_tmp;
--- a/sql/item_subselect.cc
+++ b/sql/item_subselect.cc
@ -889,6 +889,15 @@ void Item_maxmin_subselect::print(String *str, enum_query_type query_type)
 }


+void Item_maxmin_subselect::no_rows_in_result()
+{
+  value= 0;
+  null_value= 0;
+  was_values= 0;
+  make_const();
+}
+
+
 void Item_singlerow_subselect::reset()
 {
  Item_subselect::reset();
@ -1084,6 +1093,8 @@ void Item_singlerow_subselect::bring_value()
 double Item_singlerow_subselect::val_real()
 {
  DBUG_ASSERT(fixed == 1);
+  if (forced_const)
+    return value->val_real();
  if (!exec() && !value->null_value)
  {
    null_value= FALSE;
@ -1099,6 +1110,8 @@ double Item_singlerow_subselect::val_real()
 longlong Item_singlerow_subselect::val_int()
 {
  DBUG_ASSERT(fixed == 1);
+  if (forced_const)
+    return value->val_int();
  if (!exec() && !value->null_value)
  {
    null_value= FALSE;
@ -1113,6 +1126,9 @@ longlong Item_singlerow_subselect::val_int()

 String *Item_singlerow_subselect::val_str(String *str)
 {
+  DBUG_ASSERT(fixed == 1);
+  if (forced_const)
+    return value->val_str(str);
  if (!exec() && !value->null_value)
  {
    null_value= FALSE;
@ -1128,6 +1144,9 @@ String *Item_singlerow_subselect::val_str(String *str)

 my_decimal *Item_singlerow_subselect::val_decimal(my_decimal *decimal_value)
 {
+  DBUG_ASSERT(fixed == 1);
+  if (forced_const)
+    return value->val_decimal(decimal_value);
  if (!exec() && !value->null_value)
  {
    null_value= FALSE;
@ -1143,6 +1162,9 @@ my_decimal *Item_singlerow_subselect::val_decimal(my_decimal *decimal_value)

 bool Item_singlerow_subselect::val_bool()
 {
+  DBUG_ASSERT(fixed == 1);
+  if (forced_const)
+    return value->val_bool();
  if (!exec() && !value->null_value)
  {
    null_value= FALSE;
@ -1312,10 +1334,17 @@ Item* Item_exists_subselect::expr_cache_insert_transformer(uchar *thd_arg)
 }


+void Item_exists_subselect::no_rows_in_result()
+{
+  value= 0;
+  null_value= 0;
+  make_const();
+}
+
 double Item_exists_subselect::val_real()
 {
  DBUG_ASSERT(fixed == 1);
-  if (exec())
+  if (!forced_const && exec())
  {
    reset();
    return 0;
@ -1326,7 +1355,7 @@ double Item_exists_subselect::val_real()
 longlong Item_exists_subselect::val_int()
 {
  DBUG_ASSERT(fixed == 1);
-  if (exec())
+  if (!forced_const && exec())
  {
    reset();
    return 0;
@ -1351,7 +1380,7 @@ longlong Item_exists_subselect::val_int()
 String *Item_exists_subselect::val_str(String *str)
 {
  DBUG_ASSERT(fixed == 1);
-  if (exec())
+  if (!forced_const && exec())
    reset();
  str->set((ulonglong)value,&my_charset_bin);
  return str;
@ -1374,7 +1403,7 @@ String *Item_exists_subselect::val_str(String *str)
 my_decimal *Item_exists_subselect::val_decimal(my_decimal *decimal_value)
 {
  DBUG_ASSERT(fixed == 1);
-  if (exec())
+  if (!forced_const && exec())
    reset();
  int2my_decimal(E_DEC_FATAL_ERROR, value, 0, decimal_value);
  return decimal_value;
@ -1384,7 +1413,7 @@ my_decimal *Item_exists_subselect::val_decimal(my_decimal *decimal_value)
 bool Item_exists_subselect::val_bool()
 {
  DBUG_ASSERT(fixed == 1);
-  if (exec())
+  if (!forced_const && exec())
  {
    reset();
    return 0;
@ -2649,6 +2678,15 @@ void Item_allany_subselect::print(String *str, enum_query_type query_type)
 }


+void Item_allany_subselect::no_rows_in_result()
+{
+  value= 0;
+  null_value= 0;
+  was_null= 0;
+  make_const();
+}
+
+
 void subselect_engine::set_thd(THD *thd_arg)
 {
  thd= thd_arg;
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@ -146,6 +146,11 @@ public:
    eliminated= FALSE;
    null_value= 1;
  }
+  /**
+    Set the subquery result to the default value for the predicate when the
+    subquery is known to produce an empty result.
+  */
+  void no_rows_in_result()= 0;
  virtual bool select_transformer(JOIN *join);
  bool assigned() { return value_assigned; }
  void assigned(bool a) { value_assigned= a; }
@ -262,6 +267,7 @@ public:
  subs_type substype() { return SINGLEROW_SUBS; }

  void reset();
+  void no_rows_in_result() { reset(); make_const(); }
  bool select_transformer(JOIN *join);
  void store(uint i, Item* item);
  double val_real();
@ -314,6 +320,7 @@ public:
  bool any_value() { return was_values; }
  void register_value() { was_values= TRUE; }
  void reset_value_registration() { was_values= FALSE; }
+  void no_rows_in_result();
 };

 /* exists subselect */
@ -335,6 +342,7 @@ public:
    eliminated= FALSE;
    value= 0;
  }
+  void no_rows_in_result();

  enum Item_result result_type() const { return INT_RESULT;}
  longlong val_int();
@ -664,6 +672,7 @@ public:
  virtual void print(String *str, enum_query_type query_type);
  bool is_maxmin_applicable(JOIN *join);
  bool transform_into_max_min(JOIN *join);
+  void no_rows_in_result();
 };


--- a/sql/opt_subselect.cc
+++ b/sql/opt_subselect.cc
@ -5450,8 +5450,8 @@ bool JOIN::choose_tableless_subquery_plan()
    /*
      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.
+      either of TRUE, FALSE or NULL. The implementation of
+      Item_subselect::no_rows_in_result() determines which one.
    */
    if (zero_result_cause)
    {
@ -5459,14 +5459,13 @@ bool JOIN::choose_tableless_subquery_plan()
      {
        /*
          Both group by queries and non-group by queries without aggregate
-          functions produce empty subquery result.
+          functions produce empty subquery result. There is no need to further
+          rewrite the subquery because it will not be executed at all.
        */
-        subs_predicate->reset();
-        subs_predicate->make_const();
        return FALSE;
      }

-      /* TODO:
+      /* @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
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@ -3115,6 +3115,11 @@ bool st_select_lex::optimize_unflattened_subqueries()
          continue;
      }

+      bool empty_union_result= true;
+      /*
+        If the subquery is a UNION, optimize all the subqueries in the UNION. If
+        there is no UNION, then the loop will execute once for the subquery.
+      */
      for (SELECT_LEX *sl= un->first_select(); sl; sl= sl->next_select())
      {
        JOIN *inner_join= sl->join;
@ -3137,9 +3142,19 @@ bool st_select_lex::optimize_unflattened_subqueries()
        res= inner_join->optimize();
        inner_join->select_options= save_options;
        un->thd->lex->current_select= save_select;
+        if (empty_union_result)
+        {
+          /*
+            If at least one subquery in a union is non-empty, the UNION result
+            is non-empty. If there is no UNION, the only subquery is non-empy.
+          */
+          empty_union_result= inner_join->empty_result();
+        }
        if (res)
          return TRUE;
      }
+      if (empty_union_result)
+        subquery_predicate->no_rows_in_result();
    }
  }
  return FALSE;
--- a/sql/sql_select.h
+++ b/sql/sql_select.h
@ -1322,6 +1322,7 @@ public:
    return (do_send_rows && implicit_grouping && !group_optimized_away &&
            having_value != Item::COND_FALSE);
  }
+  bool empty_result() { return (zero_result_cause && !implicit_grouping); }
  bool change_result(select_result *result);
  bool is_top_level_join() const
  {