Fixed bug #52636.

Applied the fix for bug #47217 from the mysql-6.0 codebase.
The patch adds not null predicates generated for the left parts
of the equality predicates used for ref accesses. This is done
for such predicates both in where conditions and on conditions.
For the where conditions the not null predicates were generated
but in 5.0/5.1 they actually never were used due to some lame
merge from 4.1 to 5.0. The fix for bug #47217 made these 
predicates to be used in the condition pushed to the tables.
Yet only this patch generates not null predicates for equality
predicated from on conditions of outer joins.
This patch introduces a performance regression that can be
observed on a test case from null_key.test. The regression
will disappear after the fix for bug #57024 from mariadb-5.1
is pulled into mariadb-5.3.
The patch contains many changes in the outputs of the EXPLAIN 
commands since generated not null predicates are considered as
parts of the conditions pushed to join tables and may add
'Usingwhere' in some rows of EXPLAINs where there used
to be no such comments.

1 files changed, 7 insertions, 7 deletions

diff --git a/mysql-test/r/null_key.result b/mysql-test/r/null_key.result
index d59383f3037..027d1d2b93c 100644
--- a/mysql-test/r/null_key.result
+++ b/mysql-test/r/null_key.result
@@ -178,12 +178,12 @@ create table t2 (a int);
 insert into t2 values (7),(8);
 explain select * from t2 straight_join t1 where t1.a=t2.a and b is null;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	Using where
 1	SIMPLE	t1	ref	a,b	a	10	test.t2.a,const	2	Using where; Using index
 drop index b on t1;
 explain select * from t2,t1 where t1.a=t2.a and b is null;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	Using where
 1	SIMPLE	t1	ref	a	a	10	test.t2.a,const	2	Using where; Using index
 select * from t2,t1 where t1.a=t2.a and b is null;
 a	a	b
@@ -191,7 +191,7 @@ a	a	b
 8	8	NULL
 explain select * from t2,t1 where t1.a=t2.a and (b= 7 or b is null);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	Using where
 1	SIMPLE	t1	ref_or_null	a	a	10	test.t2.a,const	4	Using index
 select * from t2,t1 where t1.a=t2.a and (b= 7 or b is null);
 a	a	b
@@ -407,8 +407,8 @@ EXPLAIN SELECT SQL_CALC_FOUND_ROWS * FROM t1 LEFT JOIN t2 ON t1.a=t2.a
 LEFT JOIN t3 ON t2.b=t3.b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	4	
-1	SIMPLE	t2	ref	idx	idx	5	test.t1.a	1	
-1	SIMPLE	t3	ref	idx	idx	5	test.t2.b	1	Using index
+1	SIMPLE	t2	ref	idx	idx	5	test.t1.a	1	Using where
+1	SIMPLE	t3	ref	idx	idx	5	test.t2.b	1	Using where; Using index
 FLUSH STATUS ;
 SELECT SQL_CALC_FOUND_ROWS * FROM t1 LEFT JOIN t2 ON t1.a=t2.a
 LEFT JOIN t3 ON t2.b=t3.b;
@@ -423,8 +423,8 @@ FOUND_ROWS()
 SHOW STATUS LIKE "handler_read%";
 Variable_name	Value
 Handler_read_first	0
-Handler_read_key	6
-Handler_read_next	2
+Handler_read_key	8
+Handler_read_next	31942
 Handler_read_prev	0
 Handler_read_rnd	0
 Handler_read_rnd_next	5