Fix for bug lp:1006231

Analysis:

When a subquery that needs a temp table is executed during
the prepare or optimize phase of the outer query, at the end
of the subquery execution all the JOIN_TABs of the subquery
are replaced by a new JOIN_TAB that selects from the temp table.
However that temp table has no corresponding TABLE_LIST.
Once EXPLAIN execution reaches its last phase, it tries to print
the names of the subquery tables through its TABLE_LISTs, but in
the case of this bug there is no such TABLE_LIST (it is NULL),
hence a crash.

Solution:
The fix is to block subquery evaluation inside
Item_func_like::fix_fields and Item_func_like::select_optimize()
using the Item::is_expensive() test.

1 files changed, 12 insertions, 0 deletions

diff --git a/mysql-test/t/subselect_innodb.test b/mysql-test/t/subselect_innodb.test
index a0c52196412..26ff1072e30 100644
--- a/mysql-test/t/subselect_innodb.test
+++ b/mysql-test/t/subselect_innodb.test
@@ -356,4 +356,16 @@ WHERE f2 >= (
 
 drop table t1, t2, t3;
 
+--echo #
+--echo # LP BUG#1006231 crash in select_describe
+--echo #
+
+create table t1(a1 int) ENGINE=InnoDB;
+insert into t1 values (1);
+explain
+select 1 from t1 where 1 like (select 1 from t1 where 1 <=> (select 1 from t1 group by a1));
+select 1 from t1 where 1 like (select 1 from t1 where 1 <=> (select 1 from t1 group by a1));
+drop table t1;
+
+
 set optimizer_switch=@subselect_innodb_tmp;