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.

mysql-test/r/subselect_innodb.result

@@ -365,4 +365,19 @@ GROUP BY 1
 MAX( f1 )
 NULL
 drop table t1, t2, t3;
+#
+# LP BUG#1006231 crash in select_describe
+#
+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));
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	1	
+2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	1	
+3	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	1	Using temporary; Using filesort
+select 1 from t1 where 1 like (select 1 from t1 where 1 <=> (select 1 from t1 group by a1));
+1
+1
+drop table t1;
 set optimizer_switch=@subselect_innodb_tmp;

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;

sql/item_cmpfunc.cc

@@ -4656,7 +4656,7 @@ longlong Item_func_like::val_int()
 
 Item_func::optimize_type Item_func_like::select_optimize() const
 {
-  if (args[1]->const_item())
+  if (args[1]->const_item() && !args[1]->is_expensive())
   {
     String* res2= args[1]->val_str((String *)&cmp.value2);
     const char *ptr2;
@@ -4743,7 +4743,8 @@ bool Item_func_like::fix_fields(THD *thd, Item **ref)
       We could also do boyer-more for non-const items, but as we would have to
       recompute the tables for each row it's not worth it.
     */
-    if (args[1]->const_item() && !use_strnxfrm(collation.collation))
+    if (args[1]->const_item() && !use_strnxfrm(collation.collation) &&
+        !args[1]->is_expensive())
     {
       String* res2 = args[1]->val_str(&cmp.value2);
       if (!res2)