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, 1 insertions, 1 deletions

diff --git a/mysql-test/r/distinct.result b/mysql-test/r/distinct.result
index ee8f9f897ad..6e9150f2a06 100644
--- a/mysql-test/r/distinct.result
+++ b/mysql-test/r/distinct.result
@@ -173,7 +173,7 @@ INSERT INTO t2 values (1),(2),(3);
 INSERT INTO t3 VALUES (1,'1'),(2,'2'),(1,'1'),(2,'2');
 explain SELECT distinct t3.a FROM t3,t2,t1 WHERE t3.a=t1.b AND t1.a=t2.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ALL	PRIMARY	NULL	NULL	NULL	4	Using temporary
+1	SIMPLE	t1	ALL	PRIMARY	NULL	NULL	NULL	4	Using where; Using temporary
 1	SIMPLE	t3	ref	a	a	5	test.t1.b	2	Using index
 1	SIMPLE	t2	index	a	a	4	NULL	5	Using where; Using index; Distinct; Using join buffer
 SELECT distinct t3.a FROM t3,t2,t1 WHERE t3.a=t1.b AND t1.a=t2.a;