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, 1 insertions, 1 deletions

diff --git a/mysql-test/r/group_min_max.result b/mysql-test/r/group_min_max.result
index 20b0c054480..0b3df689089 100644
--- a/mysql-test/r/group_min_max.result
+++ b/mysql-test/r/group_min_max.result
@@ -2412,7 +2412,7 @@ EXPLAIN SELECT 1 FROM t1 AS t1_outer1 JOIN t1 AS t1_outer2
 ON t1_outer1.a = (SELECT max(b) FROM t1 GROUP BY a HAVING a < 2) 
 AND t1_outer1.b = t1_outer2.b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1_outer1	ref	a	a	5	const	1	Using where; Using index
+1	PRIMARY	t1_outer1	ref	a	a	5	const	1	Using index
 1	PRIMARY	t1_outer2	index	NULL	a	10	NULL	15	Using where; Using index; Using join buffer (flat, BNL join)
 2	SUBQUERY	t1	range	NULL	a	5	NULL	8	Using index for group-by
 EXPLAIN SELECT (SELECT (SELECT max(b) FROM t1 GROUP BY a HAVING a < 2) x