diff --git a/mysql-test/extra/rpl_tests/rpl_get_master_version_and_clock.test b/mysql-test/extra/rpl_tests/rpl_get_master_version_and_clock.test
index 89c136d8893..c392686454d 100644
--- a/mysql-test/extra/rpl_tests/rpl_get_master_version_and_clock.test
+++ b/mysql-test/extra/rpl_tests/rpl_get_master_version_and_clock.test
@@ -3,26 +3,53 @@
 # The common part of the "rpl_get_master_version_and_clock" test. 
 # Restart slave under network disconnection between slave and master
 # following the steps:
-#    1 - Got DBUG_SYNC_POINT lock
-#    2 - Set DBUG_SYNC_POINT before call mysql_real_query(...) function in get_master_version_and_clock(...) function and hang here
-#    3 - shutdown master server for simulating network disconnection
-#    4 - Release DBUG_SYNC_POINT lock
-#    5 - Check if the slave I/O thread tries to reconnect to master. 
+#    0 - Set DEBUG_SYNC_ACTION to wait 
+#        before call mysql_real_query(...) function in get_master_version_and_clock(...)
+#        function and hang here
+#    1 - activate a sync-point through the $dbug_sync_point argument of the test
+#    2 - shutdown master server for simulating network disconnection
+#    3 - signal to the IO thread through $debug_sync_action to unhold from the sync-point
+#    4 - check if the slave I/O thread tries to reconnect to master. 
 #
-# Note: Please make sure initialize the $debug_lock when call the test script.
+# Note: make sure to initialize the $debug_sync_action and $dbug_sync_point
+#       before calling the test script.
 #
+# Pattern of usage:
+#
+# The caller test supplies the DBUG_EXECUTE_IF name
+#
+#    let $dbug_sync_point = 'dbug_execute_if_name';
+#
+# as well as the action list for DEBUG_SYNC
+#    
+#    let $debug_sync_action= 'now signal signal_name';
+#
+# The $dbug_sync_point becomes the value of @@global.debug generating
+# a newly started IO-slave thread's session value.
+# Notice incremental operations to add and remove dbug_execute_if_name
+# from the global variable allows propagation more dbug arguments
+# out of mtr.
+# The action list is to fire at proper time according to test logics
+# (see pp 0-4 above).
+#
+
 connection slave;
-if (`SELECT '$debug_lock' = ''`)
+if (`SELECT $debug_sync_action = ''`)
 {
-    --die Cannot continue. Please set value for $debug_lock.
+    --die Cannot continue. Please set value for debug_sync_action.
 }
 
 # Restart slave
 --disable_warnings
 stop slave;
 source include/wait_for_slave_to_stop.inc;
+
+eval SET @@global.debug= "+d,$dbug_sync_point";
+
 start slave;
 source include/wait_for_slave_to_start.inc;
+--echo slave is going to hang in get_master_version_and_clock
+
 connection master;
 # Write file to make mysql-test-run.pl expect the "crash", but don't start
 # it until it's told to
@@ -35,7 +62,9 @@ EOF
 shutdown_server 10;
 
 connection slave;
-eval SELECT RELEASE_LOCK($debug_lock);
+--echo slave is unblocked
+
+eval SET DEBUG_SYNC=$debug_sync_action;
 
 # Show slave last IO errno
 connection slave;
@@ -53,6 +82,12 @@ if (`SELECT '$last_io_errno' = '2013' || # CR_SERVER_LOST
   --echo NETWORK ERROR
 }
 
+# deactivate the sync point of get_master_version_and_clock()
+# now to avoid restarting IO-thread to re-enter it.
+# There will be a new IO thread forked out with its @@session.debug
+# unset.
+eval set @@global.debug = "-d,$dbug_sync_point";
+
 # Write file to make mysql-test-run.pl start up the server again
 --append_file $MYSQLTEST_VARDIR/tmp/mysqld.1.expect
 restart
diff --git a/mysql-test/include/min_null_cond.inc b/mysql-test/include/min_null_cond.inc
index fcfaad43e57..c958fc7075a 100644
--- a/mysql-test/include/min_null_cond.inc
+++ b/mysql-test/include/min_null_cond.inc
@@ -18,11 +18,13 @@ EXPLAIN
 SELECT MIN( a ) FROM t1 WHERE a < NULL;
 SELECT MIN( a ) FROM t1 WHERE a < NULL;
 
+if (!$skip_null_safe_test)
+{
 --replace_column 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x
 EXPLAIN
 SELECT MIN( a ) FROM t1 WHERE a <=> NULL;
 SELECT MIN( a ) FROM t1 WHERE a <=> NULL;
-
+}
 --replace_column 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x
 EXPLAIN
 SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND 10;
diff --git a/mysql-test/r/group_min_max.result b/mysql-test/r/group_min_max.result
index 604e93af4a0..01f27a498ef 100644
--- a/mysql-test/r/group_min_max.result
+++ b/mysql-test/r/group_min_max.result
@@ -2691,6 +2691,17 @@ DROP TABLE t1;
 ## Test for NOT NULLs
 CREATE TABLE t1 ( a INT NOT NULL PRIMARY KEY);
 INSERT INTO t1 VALUES (1), (2), (3);
+#
+# NULL-safe operator test disabled for non-NULL indexed columns.
+#
+# See bugs
+#
+# - Bug#52173: Reading NULL value from non-NULL index gives
+#   wrong result in embedded server 
+#
+# - Bug#52174: Sometimes wrong plan when reading a MAX value from 
+#   non-NULL index
+#
 EXPLAIN
 SELECT MIN( a ) FROM t1 WHERE a = NULL;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
@@ -2720,13 +2731,6 @@ SELECT MIN( a ) FROM t1 WHERE a < NULL;
 MIN( a )
 NULL
 EXPLAIN
-SELECT MIN( a ) FROM t1 WHERE a <=> NULL;
-id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-x	x	x	x	x	x	x	x	x	No matching min/max row
-SELECT MIN( a ) FROM t1 WHERE a <=> NULL;
-MIN( a )
-NULL
-EXPLAIN
 SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
diff --git a/mysql-test/r/having.result b/mysql-test/r/having.result
index 9568ef88786..95893510987 100644
--- a/mysql-test/r/having.result
+++ b/mysql-test/r/having.result
@@ -450,4 +450,39 @@ HAVING amount > 0
 ORDER BY t1.id1;
 id1	amount
 DROP TABLE t1;
+#
+# Bug#48916 Server incorrectly processing HAVING clauses with an ORDER BY clause
+#
+CREATE TABLE t1 (f1 INT PRIMARY KEY, f2 INT, f3 INT);
+INSERT INTO t1 VALUES (2,7,9), (4,7,9), (6,2,9), (17,0,9);
+SELECT table1.f1, table2.f2
+FROM t1 AS table1
+JOIN t1 AS table2 ON table1.f3 = table2.f3
+WHERE table2.f1 = 2
+GROUP BY table1.f1, table2.f2
+HAVING (table2.f2 = 8 AND table1.f1 >= 6);
+f1	f2
+EXPLAIN EXTENDED
+SELECT table1.f1, table2.f2
+FROM t1 AS table1
+JOIN t1 AS table2 ON table1.f3 = table2.f3
+WHERE table2.f1 = 2
+GROUP BY table1.f1, table2.f2
+HAVING (table2.f2 = 8 AND table1.f1 >= 6);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible HAVING noticed after reading const tables
+Warnings:
+Note	1003	select `test`.`table1`.`f1` AS `f1`,'7' AS `f2` from `test`.`t1` `table1` join `test`.`t1` `table2` where ((`test`.`table1`.`f3` = '9')) group by `test`.`table1`.`f1`,'7' having (('7' = 8) and (`test`.`table1`.`f1` >= 6))
+EXPLAIN EXTENDED
+SELECT table1.f1, table2.f2
+FROM t1 AS table1
+JOIN t1 AS table2 ON table1.f3 = table2.f3
+WHERE table2.f1 = 2
+GROUP BY table1.f1, table2.f2
+HAVING (table2.f2 = 8);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible HAVING noticed after reading const tables
+Warnings:
+Note	1003	select `test`.`table1`.`f1` AS `f1`,'7' AS `f2` from `test`.`t1` `table1` join `test`.`t1` `table2` where ((`test`.`table1`.`f3` = '9')) group by `test`.`table1`.`f1`,'7' having ('7' = 8)
+DROP TABLE t1;
 End of 5.0 tests
diff --git a/mysql-test/r/join_outer.result b/mysql-test/r/join_outer.result
index 083be3737f7..4543446e807 100644
--- a/mysql-test/r/join_outer.result
+++ b/mysql-test/r/join_outer.result
@@ -1289,3 +1289,23 @@ a	COUNT( t2.b )	SUM( t2.b )	MAX( t2.b )
 1	3	6	3
 NULL	3	6	3
 DROP TABLE t1, t2;
+#
+# Bug#51598 Inconsistent behaviour with a COALESCE statement inside an IN comparison
+#
+CREATE TABLE t1(f1 INT, f2 INT, f3 INT);
+INSERT INTO t1 VALUES (1, NULL, 3);
+CREATE TABLE t2(f1 INT, f2 INT);
+INSERT INTO t2 VALUES (2, 1);
+EXPLAIN EXTENDED SELECT * FROM t1 LEFT JOIN t2 ON t1.f2 = t2.f2
+WHERE (COALESCE(t1.f1, t2.f1), f3) IN ((1, 3), (2, 2));
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	100.00	
+1	SIMPLE	t2	system	NULL	NULL	NULL	NULL	1	100.00	
+Warnings:
+Note	1003	select '1' AS `f1`,NULL AS `f2`,'3' AS `f3`,NULL AS `f1`,NULL AS `f2` from `test`.`t1` left join `test`.`t2` on(multiple equal(NULL)) where ((coalesce('1',NULL),'3') in ((1,3),(2,2)))
+SELECT * FROM t1 LEFT JOIN t2 ON t1.f2 = t2.f2
+WHERE (COALESCE(t1.f1, t2.f1), f3) IN ((1, 3), (2, 2));
+f1	f2	f3	f1	f2
+1	NULL	3	NULL	NULL
+DROP TABLE t1, t2;
+End of 5.1 tests
diff --git a/mysql-test/r/merge.result b/mysql-test/r/merge.result
index 184cd92e053..dbffbba1b8b 100644
--- a/mysql-test/r/merge.result
+++ b/mysql-test/r/merge.result
@@ -2286,4 +2286,16 @@ m1	CREATE TABLE `m1` (
 DROP TABLE m1;
 DROP TABLE `test@1`.`t@1`;
 DROP DATABASE `test@1`;
+#
+# Bug#51494c rash with join, explain and 'sounds like' operator
+#
+CREATE TABLE t1 (a INT) ENGINE=MYISAM;
+INSERT INTO t1 VALUES(1);
+CREATE TABLE t2 (b INT NOT NULL,c INT,d INT,e BLOB NOT NULL,
+KEY idx0 (d, c)) ENGINE=MERGE;
+EXPLAIN SELECT * FROM t1 NATURAL RIGHT JOIN
+t2 WHERE b SOUNDS LIKE e AND d = 1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+DROP TABLE t2, t1;
 End of 5.1 tests
diff --git a/mysql-test/r/type_year.result b/mysql-test/r/type_year.result
index 56b326327c6..8948214f565 100644
--- a/mysql-test/r/type_year.result
+++ b/mysql-test/r/type_year.result
@@ -309,4 +309,36 @@ yyyy	c4
 2069	2069
 DROP TABLE t2, t4;
 #
+# Bug #49910: Behavioural change in SELECT/WHERE on YEAR(4) data type
+#
+CREATE TABLE t1 (y YEAR NOT NULL, s VARCHAR(4));
+INSERT INTO t1 (s) VALUES ('bad');
+Warnings:
+Warning	1364	Field 'y' doesn't have a default value
+INSERT INTO t1 (y, s) VALUES (0, 0), (2000, 2000), (2001, 2001);
+SELECT * FROM t1 ta, t1 tb WHERE ta.y = tb.y;
+y	s	y	s
+0000	bad	0000	bad
+0000	0	0000	bad
+0000	bad	0000	0
+0000	0	0000	0
+2000	2000	2000	2000
+2001	2001	2001	2001
+SELECT * FROM t1 WHERE t1.y = 0;
+y	s
+0000	bad
+0000	0
+SELECT * FROM t1 WHERE t1.y = 2000;
+y	s
+2000	2000
+SELECT ta.y AS ta_y, ta.s, tb.y AS tb_y, tb.s FROM t1 ta, t1 tb HAVING ta_y = tb_y;
+ta_y	s	tb_y	s
+0000	bad	0000	bad
+0000	0	0000	bad
+0000	bad	0000	0
+0000	0	0000	0
+2000	2000	2000	2000
+2001	2001	2001	2001
+DROP TABLE t1;
+#
 End of 5.1 tests
diff --git a/mysql-test/suite/rpl/r/rpl_get_master_version_and_clock.result b/mysql-test/suite/rpl/r/rpl_get_master_version_and_clock.result
index d054cb573d3..a34c536feb8 100644
--- a/mysql-test/suite/rpl/r/rpl_get_master_version_and_clock.result
+++ b/mysql-test/suite/rpl/r/rpl_get_master_version_and_clock.result
@@ -7,34 +7,24 @@ start slave;
 call mtr.add_suppression("Slave I/O: Master command COM_REGISTER_SLAVE failed: .*");
 call mtr.add_suppression("Fatal error: The slave I/O thread stops because master and slave have equal MySQL server ids; .*");
 call mtr.add_suppression("Slave I/O thread .* register on master");
-SELECT IS_FREE_LOCK("debug_lock.before_get_UNIX_TIMESTAMP");
-IS_FREE_LOCK("debug_lock.before_get_UNIX_TIMESTAMP")
-1
-SELECT GET_LOCK("debug_lock.before_get_UNIX_TIMESTAMP", 1000);
-GET_LOCK("debug_lock.before_get_UNIX_TIMESTAMP", 1000)
-1
-set global debug= 'd,debug_lock.before_get_UNIX_TIMESTAMP';
 stop slave;
+SET @@global.debug= "+d,'debug_lock.before_get_UNIX_TIMESTAMP'";
 start slave;
-SELECT RELEASE_LOCK("debug_lock.before_get_UNIX_TIMESTAMP");
-RELEASE_LOCK("debug_lock.before_get_UNIX_TIMESTAMP")
-1
+slave is going to hang in get_master_version_and_clock
+slave is unblocked
+SET DEBUG_SYNC='now SIGNAL signal.get_unix_timestamp';
 Check network error happened here
 NETWORK ERROR
-SELECT IS_FREE_LOCK("debug_lock.before_get_SERVER_ID");
-IS_FREE_LOCK("debug_lock.before_get_SERVER_ID")
-1
-SELECT GET_LOCK("debug_lock.before_get_SERVER_ID", 1000);
-GET_LOCK("debug_lock.before_get_SERVER_ID", 1000)
-1
-set global debug= 'd,debug_lock.before_get_SERVER_ID';
+set @@global.debug = "-d,'debug_lock.before_get_UNIX_TIMESTAMP'";
 stop slave;
+SET @@global.debug= "+d,'debug_lock.before_get_SERVER_ID'";
 start slave;
-SELECT RELEASE_LOCK("debug_lock.before_get_SERVER_ID");
-RELEASE_LOCK("debug_lock.before_get_SERVER_ID")
-1
+slave is going to hang in get_master_version_and_clock
+slave is unblocked
+SET DEBUG_SYNC='now SIGNAL signal.get_server_id';
 Check network error happened here
 NETWORK ERROR
+set @@global.debug = "-d,'debug_lock.before_get_SERVER_ID'";
 set global debug= '';
 reset master;
 include/stop_slave.inc
@@ -43,3 +33,4 @@ start slave;
 *** must be having the replicate-same-server-id IO thread error ***
 Slave_IO_Errno= 1593
 Slave_IO_Error= Fatal error: The slave I/O thread stops because master and slave have equal MySQL server ids; these ids must be different for replication to work (or the --replicate-same-server-id option must be used on slave but this does not always make sense; please check the manual before using it).
+SET DEBUG_SYNC= 'RESET';
diff --git a/mysql-test/suite/rpl/r/rpl_show_slave_running.result b/mysql-test/suite/rpl/r/rpl_show_slave_running.result
index da26190e76d..598762d5188 100644
--- a/mysql-test/suite/rpl/r/rpl_show_slave_running.result
+++ b/mysql-test/suite/rpl/r/rpl_show_slave_running.result
@@ -4,11 +4,9 @@ reset master;
 reset slave;
 drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
 start slave;
+SET DEBUG_SYNC= 'RESET';
 include/stop_slave.inc
-SELECT GET_LOCK("debug_lock.before_get_running_status_yes", 1000);
-GET_LOCK("debug_lock.before_get_running_status_yes", 1000)
-1
-set global debug= 'd,debug_lock.before_get_running_status_yes';
+set global debug= 'd,dbug.before_get_running_status_yes';
 Slave_running, Slave_IO_Running, Slave_SQL_Running, must be OFF, NO, NO in three following queries
 SHOW STATUS LIKE 'Slave_running';
 Variable_name	Value
@@ -22,9 +20,7 @@ Variable_name	Value
 Slave_running	OFF
 Slave_IO_Running= No
 Slave_SQL_Running= No
-SELECT RELEASE_LOCK("debug_lock.before_get_running_status_yes");
-RELEASE_LOCK("debug_lock.before_get_running_status_yes")
-1
+SET DEBUG_SYNC='now SIGNAL signal.io_thread_let_running';
 Slave_running, Slave_IO_Running, Slave_SQL_Running must be OFF YES NO in three following queries
 SHOW STATUS LIKE 'Slave_running';
 Variable_name	Value
@@ -39,4 +35,5 @@ Slave_running	ON
 Slave_IO_Running= Yes
 Slave_SQL_Running= Yes
 set global debug= '';
+SET DEBUG_SYNC= 'RESET';
 End of tests
diff --git a/mysql-test/suite/rpl/t/rpl_get_master_version_and_clock.test b/mysql-test/suite/rpl/t/rpl_get_master_version_and_clock.test
index 24309e8a14a..4a9276d9880 100644
--- a/mysql-test/suite/rpl/t/rpl_get_master_version_and_clock.test
+++ b/mysql-test/suite/rpl/t/rpl_get_master_version_and_clock.test
@@ -16,8 +16,16 @@
 
 source include/master-slave.inc;
 source include/have_debug.inc;
+source include/have_debug_sync.inc;
+
+#
+# The test is not supposed to have any binglog affairs.
+# Hence it's enough it to run only with one binlog format
+#
+source include/have_binlog_format_mixed.inc;
 
 connection slave;
+
 call mtr.add_suppression("Slave I/O: Master command COM_REGISTER_SLAVE failed: .*");
 call mtr.add_suppression("Fatal error: The slave I/O thread stops because master and slave have equal MySQL server ids; .*");
 call mtr.add_suppression("Slave I/O thread .* register on master");
@@ -25,20 +33,16 @@ call mtr.add_suppression("Slave I/O thread .* register on master");
 #Test case 1: Try to get the value of the UNIX_TIMESTAMP from master under network disconnection
 let $debug_saved= `select @@global.debug`;
 
-let $debug_lock= "debug_lock.before_get_UNIX_TIMESTAMP";
-eval SELECT IS_FREE_LOCK($debug_lock);
-eval SELECT GET_LOCK($debug_lock, 1000);
-
-set global debug= 'd,debug_lock.before_get_UNIX_TIMESTAMP';
+# set up two parameters to pass into extra/rpl_tests/rpl_get_master_version_and_clock
+let $dbug_sync_point= 'debug_lock.before_get_UNIX_TIMESTAMP';
+let $debug_sync_action= 'now SIGNAL signal.get_unix_timestamp';
 source extra/rpl_tests/rpl_get_master_version_and_clock.test; 
 
 #Test case 2: Try to get the value of the SERVER_ID from master under network disconnection
 connection slave;
-let $debug_lock= "debug_lock.before_get_SERVER_ID";
-eval SELECT IS_FREE_LOCK($debug_lock);
-eval SELECT GET_LOCK($debug_lock, 1000);
 
-set global debug= 'd,debug_lock.before_get_SERVER_ID';
+let $dbug_sync_point= 'debug_lock.before_get_SERVER_ID';
+let $debug_sync_action= 'now SIGNAL signal.get_server_id';
 source extra/rpl_tests/rpl_get_master_version_and_clock.test;
 
 eval set global debug= '$debug_saved';
@@ -62,4 +66,9 @@ let $last_io_error= query_get_value("show slave status", Last_IO_Error, 1);
 echo Slave_IO_Errno= $last_io_errno;
 echo Slave_IO_Error= $last_io_error;
 
+# cleanup
+
+# is not really necessary but avoids mtr post-run env check warnings
+SET DEBUG_SYNC= 'RESET';
+
 # End of tests
diff --git a/mysql-test/suite/rpl/t/rpl_show_slave_running.test b/mysql-test/suite/rpl/t/rpl_show_slave_running.test
index 62cc311e6b2..8a3e56975ad 100644
--- a/mysql-test/suite/rpl/t/rpl_show_slave_running.test
+++ b/mysql-test/suite/rpl/t/rpl_show_slave_running.test
@@ -5,14 +5,14 @@
 #
 source include/master-slave.inc;
 source include/have_debug.inc;
+source include/have_debug_sync.inc;
 
 connection slave;
-
+SET DEBUG_SYNC= 'RESET';
 source include/stop_slave.inc;
 let $debug_saved= `select @@global.debug`;
-let $debug_lock= "debug_lock.before_get_running_status_yes";
-eval SELECT GET_LOCK($debug_lock, 1000);
-set global debug= 'd,debug_lock.before_get_running_status_yes';
+set global debug= 'd,dbug.before_get_running_status_yes'; # to block due-started IO
+
 
 # Test 1. Slave is stopped
 
@@ -29,6 +29,12 @@ echo Slave_SQL_Running= $status;
 
 start slave io_thread;
 
+#
+# Notice a difference between versions in showing p.2: 
+# 5.1 has two OFF,ON IO-thread state running state whereas later versions
+# have three: OFF,Connecting,ON.
+# Hence, 5.1 must display OFF NO NO where as 5.1+ OFF Connecting NO
+#
 --echo Slave_running, Slave_IO_Running, Slave_SQL_Running must be OFF NO NO in three following queries
 
 SHOW STATUS LIKE 'Slave_running';
@@ -40,7 +46,7 @@ echo Slave_SQL_Running= $status;
 # Test 3. The slave IO thread is started and got connected to master
 #         and SQL thread is still not started
 
-eval SELECT RELEASE_LOCK($debug_lock);
+SET DEBUG_SYNC='now SIGNAL signal.io_thread_let_running'; # unblock IO thread now
 let $slave_param= Slave_IO_Running;
 let $slave_param_value= YES;
 source include/wait_for_slave_param.inc;
@@ -72,5 +78,5 @@ echo Slave_SQL_Running= $status;
 connection slave;
 
 eval set global debug= '$debug_saved';
-
+SET DEBUG_SYNC= 'RESET';
 --echo End of tests
diff --git a/mysql-test/t/group_min_max.test b/mysql-test/t/group_min_max.test
index 6aec0e3677f..b06f0c09fc5 100644
--- a/mysql-test/t/group_min_max.test
+++ b/mysql-test/t/group_min_max.test
@@ -1070,6 +1070,18 @@ DROP TABLE t1;
 --echo ## Test for NOT NULLs
 CREATE TABLE t1 ( a INT NOT NULL PRIMARY KEY);
 INSERT INTO t1 VALUES (1), (2), (3);
+--echo #
+--echo # NULL-safe operator test disabled for non-NULL indexed columns.
+--echo #
+--echo # See bugs
+--echo #
+--echo # - Bug#52173: Reading NULL value from non-NULL index gives
+--echo #   wrong result in embedded server 
+--echo #
+--echo # - Bug#52174: Sometimes wrong plan when reading a MAX value from 
+--echo #   non-NULL index
+--echo #
+--let $skip_null_safe_test= 1
 --source include/min_null_cond.inc
 DROP TABLE t1;
 
diff --git a/mysql-test/t/having.test b/mysql-test/t/having.test
index 185ca4bdddb..b68ba69b975 100644
--- a/mysql-test/t/having.test
+++ b/mysql-test/t/having.test
@@ -467,5 +467,35 @@ ORDER BY t1.id1;
 
 DROP TABLE t1;
 
+--echo #
+--echo # Bug#48916 Server incorrectly processing HAVING clauses with an ORDER BY clause
+--echo #
+CREATE TABLE t1 (f1 INT PRIMARY KEY, f2 INT, f3 INT);
+INSERT INTO t1 VALUES (2,7,9), (4,7,9), (6,2,9), (17,0,9);
+
+SELECT table1.f1, table2.f2
+FROM t1 AS table1
+JOIN t1 AS table2 ON table1.f3 = table2.f3
+WHERE table2.f1 = 2
+GROUP BY table1.f1, table2.f2
+HAVING (table2.f2 = 8 AND table1.f1 >= 6);
+
+EXPLAIN EXTENDED
+SELECT table1.f1, table2.f2
+FROM t1 AS table1
+JOIN t1 AS table2 ON table1.f3 = table2.f3
+WHERE table2.f1 = 2
+GROUP BY table1.f1, table2.f2
+HAVING (table2.f2 = 8 AND table1.f1 >= 6);
+
+EXPLAIN EXTENDED
+SELECT table1.f1, table2.f2
+FROM t1 AS table1
+JOIN t1 AS table2 ON table1.f3 = table2.f3
+WHERE table2.f1 = 2
+GROUP BY table1.f1, table2.f2
+HAVING (table2.f2 = 8);
+
+DROP TABLE t1;
 
 --echo End of 5.0 tests
diff --git a/mysql-test/t/join_outer.test b/mysql-test/t/join_outer.test
index aeaa69657c6..e3d68d71603 100644
--- a/mysql-test/t/join_outer.test
+++ b/mysql-test/t/join_outer.test
@@ -896,3 +896,21 @@ FROM t1 JOIN t2 USING( a )
 GROUP BY t1.a WITH ROLLUP;
 
 DROP TABLE t1, t2;
+
+--echo #
+--echo # Bug#51598 Inconsistent behaviour with a COALESCE statement inside an IN comparison
+--echo #
+CREATE TABLE t1(f1 INT, f2 INT, f3 INT);
+INSERT INTO t1 VALUES (1, NULL, 3);
+CREATE TABLE t2(f1 INT, f2 INT);
+INSERT INTO t2 VALUES (2, 1);
+
+EXPLAIN EXTENDED SELECT * FROM t1 LEFT JOIN t2 ON t1.f2 = t2.f2
+WHERE (COALESCE(t1.f1, t2.f1), f3) IN ((1, 3), (2, 2));
+
+SELECT * FROM t1 LEFT JOIN t2 ON t1.f2 = t2.f2
+WHERE (COALESCE(t1.f1, t2.f1), f3) IN ((1, 3), (2, 2));
+
+DROP TABLE t1, t2;
+
+--echo End of 5.1 tests
diff --git a/mysql-test/t/merge.test b/mysql-test/t/merge.test
index d88467cc7a9..44b202fab97 100644
--- a/mysql-test/t/merge.test
+++ b/mysql-test/t/merge.test
@@ -1690,4 +1690,19 @@ DROP TABLE m1;
 DROP TABLE `test@1`.`t@1`;
 DROP DATABASE `test@1`;
 
+--echo #
+--echo # Bug#51494c rash with join, explain and 'sounds like' operator
+--echo #
+
+CREATE TABLE t1 (a INT) ENGINE=MYISAM;
+INSERT INTO t1 VALUES(1);
+
+CREATE TABLE t2 (b INT NOT NULL,c INT,d INT,e BLOB NOT NULL,
+KEY idx0 (d, c)) ENGINE=MERGE;
+
+EXPLAIN SELECT * FROM t1 NATURAL RIGHT JOIN
+t2 WHERE b SOUNDS LIKE e AND d = 1;
+
+DROP TABLE t2, t1;
+
 --echo End of 5.1 tests
diff --git a/mysql-test/t/type_year.test b/mysql-test/t/type_year.test
index 16fd39a59d8..d8da4ccc82c 100644
--- a/mysql-test/t/type_year.test
+++ b/mysql-test/t/type_year.test
@@ -133,6 +133,22 @@ SELECT * FROM t4 WHERE yyyy > 123;
 
 DROP TABLE t2, t4;
 
+--echo #
+--echo # Bug #49910: Behavioural change in SELECT/WHERE on YEAR(4) data type
+--echo #
+
+CREATE TABLE t1 (y YEAR NOT NULL, s VARCHAR(4));
+INSERT INTO t1 (s) VALUES ('bad');
+INSERT INTO t1 (y, s) VALUES (0, 0), (2000, 2000), (2001, 2001);
+
+SELECT * FROM t1 ta, t1 tb WHERE ta.y = tb.y;
+SELECT * FROM t1 WHERE t1.y = 0;
+SELECT * FROM t1 WHERE t1.y = 2000;
+
+SELECT ta.y AS ta_y, ta.s, tb.y AS tb_y, tb.s FROM t1 ta, t1 tb HAVING ta_y = tb_y;
+
+DROP TABLE t1;
+
 --echo #
 
 --echo End of 5.1 tests
diff --git a/sql/debug_sync.cc b/sql/debug_sync.cc
index 2580d526b52..23a649a89fa 100644
--- a/sql/debug_sync.cc
+++ b/sql/debug_sync.cc
@@ -1903,4 +1903,42 @@ void debug_sync(THD *thd, const char *sync_point_name, size_t name_len)
   DBUG_VOID_RETURN;
 }
 
+/**
+  Define debug sync action.
+
+  @param[in]        thd             thread handle
+  @param[in]        action_str      action string
+
+  @return           status
+    @retval         FALSE           ok
+    @retval         TRUE            error
+
+  @description
+    The function is similar to @c debug_sync_eval_action but is
+    to be called immediately from the server code rather than 
+    to be triggered by setting a value to DEBUG_SYNC system variable.
+
+  @note
+    The input string is copied prior to be fed to
+    @c debug_sync_eval_action to let the latter modify it.
+
+    Caution.
+    The function allocates in THD::mem_root and therefore
+    is not recommended to be deployed inside big loops.    
+*/
+
+bool debug_sync_set_action(THD *thd, const char *action_str, size_t len)
+{
+  bool                  rc;
+  char *value;
+  DBUG_ENTER("debug_sync_set_action");
+  DBUG_ASSERT(thd);
+  DBUG_ASSERT(action_str);
+  
+  value= strmake_root(thd->mem_root, action_str, len);
+  rc= debug_sync_eval_action(thd, value);
+  DBUG_RETURN(rc);
+}
+
+
 #endif /* defined(ENABLED_DEBUG_SYNC) */
diff --git a/sql/debug_sync.h b/sql/debug_sync.h
index f4cd0b364cf..9ac7da39d4d 100644
--- a/sql/debug_sync.h
+++ b/sql/debug_sync.h
@@ -50,6 +50,7 @@ extern void debug_sync_end(void);
 extern void debug_sync_init_thread(THD *thd);
 extern void debug_sync_end_thread(THD *thd);
 extern void debug_sync(THD *thd, const char *sync_point_name, size_t name_len);
+extern bool debug_sync_set_action(THD *thd, const char *action_str, size_t len);
 
 #else /* defined(ENABLED_DEBUG_SYNC) */
 
diff --git a/sql/item_cmpfunc.cc b/sql/item_cmpfunc.cc
index cd3f18fe1eb..6e38220abd1 100644
--- a/sql/item_cmpfunc.cc
+++ b/sql/item_cmpfunc.cc
@@ -1190,12 +1190,21 @@ get_year_value(THD *thd, Item ***item_arg, Item **cache_arg,
   /*
     Coerce value to the 19XX form in order to correctly compare
     YEAR(2) & YEAR(4) types.
+    Here we are converting all item values but YEAR(4) fields since
+      1) YEAR(4) already has a regular YYYY form and
+      2) we don't want to convert zero/bad YEAR(4) values to the
+         value of 2000.
   */
-  if (value < 70)
-    value+= 100;
-  if (value <= 1900)
-    value+= 1900;
-
+  Item *real_item= item->real_item();
+  if (!(real_item->type() == Item::FIELD_ITEM &&
+        ((Item_field *)real_item)->field->type() == MYSQL_TYPE_YEAR &&
+        ((Item_field *)real_item)->field->field_length == 4))
+  {
+    if (value < 70)
+      value+= 100;
+    if (value <= 1900)
+      value+= 1900;
+  }
   /* Convert year to DATETIME of form YYYY-00-00 00:00:00 (YYYY0000000000). */
   value*= 10000000000LL;
 
diff --git a/sql/item_func.cc b/sql/item_func.cc
index 845654c1881..1e31755179b 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -3362,80 +3362,6 @@ longlong Item_master_pos_wait::val_int()
   return event_count;
 }
 
-#ifdef EXTRA_DEBUG
-void debug_sync_point(const char* lock_name, uint lock_timeout)
-{
-  THD* thd=current_thd;
-  User_level_lock* ull;
-  struct timespec abstime;
-  size_t lock_name_len;
-  lock_name_len= strlen(lock_name);
-  pthread_mutex_lock(&LOCK_user_locks);
-
-  if (thd->ull)
-  {
-    item_user_lock_release(thd->ull);
-    thd->ull=0;
-  }
-
-  /*
-    If the lock has not been aquired by some client, we do not want to
-    create an entry for it, since we immediately release the lock. In
-    this case, we will not be waiting, but rather, just waste CPU and
-    memory on the whole deal
-  */
-  if (!(ull= ((User_level_lock*) hash_search(&hash_user_locks,
-                                             (uchar*) lock_name,
-                                             lock_name_len))))
-  {
-    pthread_mutex_unlock(&LOCK_user_locks);
-    return;
-  }
-  ull->count++;
-
-  /*
-    Structure is now initialized.  Try to get the lock.
-    Set up control struct to allow others to abort locks
-  */
-  thd_proc_info(thd, "User lock");
-  thd->mysys_var->current_mutex= &LOCK_user_locks;
-  thd->mysys_var->current_cond=  &ull->cond;
-
-  set_timespec(abstime,lock_timeout);
-  while (ull->locked && !thd->killed)
-  {
-    int error= pthread_cond_timedwait(&ull->cond, &LOCK_user_locks, &abstime);
-    if (error == ETIMEDOUT || error == ETIME)
-      break;
-  }
-
-  if (ull->locked)
-  {
-    if (!--ull->count)
-      delete ull;				// Should never happen
-  }
-  else
-  {
-    ull->locked=1;
-    ull->set_thread(thd);
-    thd->ull=ull;
-  }
-  pthread_mutex_unlock(&LOCK_user_locks);
-  pthread_mutex_lock(&thd->mysys_var->mutex);
-  thd_proc_info(thd, 0);
-  thd->mysys_var->current_mutex= 0;
-  thd->mysys_var->current_cond=  0;
-  pthread_mutex_unlock(&thd->mysys_var->mutex);
-  pthread_mutex_lock(&LOCK_user_locks);
-  if (thd->ull)
-  {
-    item_user_lock_release(thd->ull);
-    thd->ull=0;
-  }
-  pthread_mutex_unlock(&LOCK_user_locks);
-}
-
-#endif
 
 /**
   Get a user level lock.  If the thread has an old lock this is first released.
diff --git a/sql/item_row.cc b/sql/item_row.cc
index 29b37eb2bc0..7535c1fa80b 100644
--- a/sql/item_row.cc
+++ b/sql/item_row.cc
@@ -30,7 +30,8 @@
 */
 
 Item_row::Item_row(List<Item> &arg):
-  Item(), used_tables_cache(0), const_item_cache(1), with_null(0)
+  Item(), used_tables_cache(0), not_null_tables_cache(0),
+  const_item_cache(1), with_null(0)
 {
 
   //TODO: think placing 2-3 component items in item (as it done for function)
@@ -71,6 +72,7 @@ bool Item_row::fix_fields(THD *thd, Item **ref)
     Item *item= *arg;
     used_tables_cache |= item->used_tables();
     const_item_cache&= item->const_item() && !with_null;
+    not_null_tables_cache|= item->not_null_tables();
     /*
       Some subqueries transformations aren't done in the view_prepare_mode thus
       is_null() will fail. So we skip is_null() calculation for CREATE VIEW as
diff --git a/sql/item_row.h b/sql/item_row.h
index 67441f49603..76d1c875e7d 100644
--- a/sql/item_row.h
+++ b/sql/item_row.h
@@ -16,7 +16,7 @@
 class Item_row: public Item
 {
   Item **items;
-  table_map used_tables_cache;
+  table_map used_tables_cache, not_null_tables_cache;
   uint arg_count;
   bool const_item_cache;
   bool with_null;
@@ -26,6 +26,7 @@ public:
     Item(),
     items(item->items),
     used_tables_cache(item->used_tables_cache),
+    not_null_tables_cache(0),
     arg_count(item->arg_count),
     const_item_cache(item->const_item_cache),
     with_null(0)
@@ -65,6 +66,7 @@ public:
   bool const_item() const { return const_item_cache; };
   enum Item_result result_type() const { return ROW_RESULT; }
   void update_used_tables();
+  table_map not_null_tables() const { return not_null_tables_cache; }
   virtual void print(String *str, enum_query_type query_type);
 
   bool walk(Item_processor processor, bool walk_subquery, uchar *arg);
diff --git a/sql/mysql_priv.h b/sql/mysql_priv.h
index 90b02f5337a..098ea514cb6 100644
--- a/sql/mysql_priv.h
+++ b/sql/mysql_priv.h
@@ -580,20 +580,6 @@ protected:
 
 /* Used to check GROUP BY list in the MODE_ONLY_FULL_GROUP_BY mode */
 #define UNDEF_POS (-1)
-#ifdef EXTRA_DEBUG
-/**
-  Sync points allow us to force the server to reach a certain line of code
-  and block there until the client tells the server it is ok to go on.
-  The client tells the server to block with SELECT GET_LOCK()
-  and unblocks it with SELECT RELEASE_LOCK(). Used for debugging difficult
-  concurrency problems
-*/
-#define DBUG_SYNC_POINT(lock_name,lock_timeout) \
- debug_sync_point(lock_name,lock_timeout)
-void debug_sync_point(const char* lock_name, uint lock_timeout);
-#else
-#define DBUG_SYNC_POINT(lock_name,lock_timeout)
-#endif /* EXTRA_DEBUG */
 
 /* BINLOG_DUMP options */
 
diff --git a/sql/slave.cc b/sql/slave.cc
index a89ac2e682b..e8405ffcd37 100644
--- a/sql/slave.cc
+++ b/sql/slave.cc
@@ -44,6 +44,7 @@
 #ifdef HAVE_REPLICATION
 
 #include "rpl_tblmap.h"
+#include "debug_sync.h"
 
 #define FLAGSTR(V,F) ((V)&(F)?#F" ":"")
 
@@ -981,7 +982,16 @@ static int get_master_version_and_clock(MYSQL* mysql, Master_info* mi)
     unavailable (very old master not supporting UNIX_TIMESTAMP()?).
   */
 
-  DBUG_SYNC_POINT("debug_lock.before_get_UNIX_TIMESTAMP", 10);
+  DBUG_EXECUTE_IF("dbug.before_get_UNIX_TIMESTAMP",
+                  {
+                    const char act[]=
+                      "now "
+                      "wait_for signal.get_unix_timestamp";
+                    DBUG_ASSERT(opt_debug_sync_timeout > 0);
+                    DBUG_ASSERT(!debug_sync_set_action(current_thd,
+                                                       STRING_WITH_LEN(act)));
+                  };);
+
   master_res= NULL;
   if (!mysql_real_query(mysql, STRING_WITH_LEN("SELECT UNIX_TIMESTAMP()")) &&
       (master_res= mysql_store_result(mysql)) &&
@@ -1020,7 +1030,15 @@ static int get_master_version_and_clock(MYSQL* mysql, Master_info* mi)
     Note: we could have put a @@SERVER_ID in the previous SELECT
     UNIX_TIMESTAMP() instead, but this would not have worked on 3.23 masters.
   */
-  DBUG_SYNC_POINT("debug_lock.before_get_SERVER_ID", 10);
+  DBUG_EXECUTE_IF("dbug.before_get_SERVER_ID",
+                  {
+                    const char act[]=
+                      "now "
+                      "wait_for signal.get_server_id";
+                    DBUG_ASSERT(opt_debug_sync_timeout > 0);
+                    DBUG_ASSERT(!debug_sync_set_action(current_thd, 
+                                                       STRING_WITH_LEN(act)));
+                  };);
   master_res= NULL;
   master_row= NULL;
   if (!mysql_real_query(mysql,
@@ -2557,7 +2575,16 @@ pthread_handler_t handle_slave_io(void *arg)
 
 connected:
 
-  DBUG_SYNC_POINT("debug_lock.before_get_running_status_yes", 10);
+    DBUG_EXECUTE_IF("dbug.before_get_running_status_yes",
+                    {
+                      const char act[]=
+                        "now "
+                        "wait_for signal.io_thread_let_running";
+                      DBUG_ASSERT(opt_debug_sync_timeout > 0);
+                      DBUG_ASSERT(!debug_sync_set_action(thd, 
+                                                         STRING_WITH_LEN(act)));
+                    };);
+
   // TODO: the assignment below should be under mutex (5.0)
   mi->slave_running= MYSQL_SLAVE_RUN_CONNECT;
   thd->slave_net = &mysql->net;
diff --git a/sql/sql_repl.cc b/sql/sql_repl.cc
index ae995ea5ed3..44215d90634 100644
--- a/sql/sql_repl.cc
+++ b/sql/sql_repl.cc
@@ -1711,7 +1711,6 @@ int log_loaded_block(IO_CACHE* file)
       if (mysql_bin_log.write(&b))
         DBUG_RETURN(1);
       lf_info->wrote_create_file= 1;
-      DBUG_SYNC_POINT("debug_lock.created_file_event",10);
     }
   }
   DBUG_RETURN(0);
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 055246ee0df..618332ae89b 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -1112,6 +1112,31 @@ JOIN::optimize()
   {
     conds=new Item_int((longlong) 0,1);	// Always false
   }
+
+  /*
+    It's necessary to check const part of HAVING cond as
+    there is a chance that some cond parts may become
+    const items after make_join_statisctics(for example
+    when Item is a reference to cost table field from
+    outer join).
+    This check is performed only for those conditions
+    which do not use aggregate functions. In such case
+    temporary table may not be used and const condition
+    elements may be lost during further having
+    condition transformation in JOIN::exec.
+  */
+  if (having && !having->with_sum_func)
+  {
+    COND *const_cond= make_cond_for_table(having, const_table_map, 0);
+    DBUG_EXECUTE("where", print_where(const_cond, "const_having_cond",
+                                      QT_ORDINARY););
+    if (const_cond && !const_cond->val_int())
+    {
+      zero_result_cause= "Impossible HAVING noticed after reading const tables";
+      DBUG_RETURN(0);
+    }
+  }
+
   if (make_join_select(this, select, conds))
   {
     zero_result_cause=
@@ -2943,7 +2968,8 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables_arg, COND *conds,
       s->quick=select->quick;
       s->needed_reg=select->needed_reg;
       select->quick=0;
-      if (records == 0 && s->table->reginfo.impossible_range)
+      if (records == 0 && s->table->reginfo.impossible_range &&
+          (s->table->file->ha_table_flags() & HA_STATS_RECORDS_IS_EXACT))
       {
 	/*
 	  Impossible WHERE or ON expression