Fix LP BUG#778413

Analysis:
The subquery is evaluated first during ref-optimization of the outer
query because the subquery is considered constant from the perspective
of the outer query. Thus an attempt is made to evaluate the MAX subquery
and use the new constant to drive an index nested loops join.
During this evaluation the inner-most subquery replaces the JOIN_TAB
with a new one that fetches the data from a temp table.
The function select_describe crashes at the lines:
        TABLE_LIST *real_table= table->pos_in_table_list; 
	item_list.push_back(new Item_string(real_table->alias,
					    strlen(real_table->alias),
					    cs));
because 'table' is a temp table, and it has no corresponding table
reference. This 'real_table' is NULL, and real_table->alias results
in a crash.

Solution:
In the spirit of MWL#89 prevent the evaluation of expensive predicates
during optimization. This patch prevents the evaluation of expensive
predicates during ref optimization.


sql/item_subselect.h:
  Remove unused class member. Not needed for the fix, but noticed now and removed.

1 files changed, 2 insertions, 2 deletions

diff --git a/mysql-test/r/subselect_no_opts.result b/mysql-test/r/subselect_no_opts.result
index 24d652b7bd8..14711c30a7f 100644
--- a/mysql-test/r/subselect_no_opts.result
+++ b/mysql-test/r/subselect_no_opts.result
@@ -371,7 +371,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 2	SUBQUERY	t8	const	PRIMARY	PRIMARY	37	const	1	100.00	
 3	SUBQUERY	t8	const	PRIMARY	PRIMARY	37		1	100.00	Using index
 Warnings:
-Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where 1) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where 1
+Note	1003	select 'joce' AS `pseudo`,(select 'test' from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))) AS `(SELECT email FROM t8 WHERE pseudo=(SELECT pseudo FROM t8 WHERE pseudo='joce'))` from `test`.`t8` where ('joce' = (select 'joce' from `test`.`t8` where 1))
 SELECT pseudo FROM t8 WHERE pseudo=(SELECT pseudo,email FROM
 t8 WHERE pseudo='joce');
 ERROR 21000: Operand should contain 1 column(s)
@@ -550,7 +550,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t1	const	PRIMARY,numreponse	PRIMARY	7	const,const	1	100.00	Using index
 2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
 Warnings:
-Note	1003	select '3' AS `numreponse` from `test`.`t1` where (('1' = '1'))
+Note	1003	select '3' AS `numreponse` from `test`.`t1` where (('1' = '1') and ('3' = 3))
 drop table t1;
 CREATE TABLE t1 (a int(1));
 INSERT INTO t1 VALUES (1);