Fix LP BUG#718763

Analysis:
The reason for the crash was that the inner subquery was executed
via a scan on a final temporary table applied after all other
operations. This final operation is implemented by changing the
contents of the JOIN object of the subquery to represent a table
scan over the temp table. At the same time query optimization of
the outer subquery required evaluation of the inner subquery, which
happened before the actual EXPLAIN. The evaluation left the JOIN
object of the inner subquery in the changed state, where it represented
a table scan over a temp table, and EXPLAIN crashed because the temp
table is not associated with any table reference (TABLE_LIST object).
The reason the JOIN was not restored was because its saving/restoration
was controlled by the join->select_lex->uncacheable flag, which was
not set in the case of materialization.

Solution:
In the methods Item_in_subselect::[single | row]_value_transformer() set:
    select_lex->uncacheable|= UNCACHEABLE_EXPLAIN;
In addition, for symmetry, change:
    master_unit->uncacheable|= UNCACHEABLE_EXPLAIN;
instead of UNCACHEABLE_DEPENDENT because if a subquery was not
dependent initially, the changed methods do not change this
fact. The subquery may later become correlated if it is transformed
to an EXISTS query, but it may stay uncorrelated if executed via
materialization.

mysql-test/r/subselect4.result

@@ -707,3 +707,42 @@ f4
 f
 d
 drop table t1,t2;
+#
+# LP BUG#718763 Second crash in select_describe() and materialization
+#
+CREATE TABLE t1 ( f1 int(11), f3 int(11), f10 varchar(1), KEY (f3)) ;
+INSERT INTO t1 VALUES ('28','6','m'),('29','4','c');
+CREATE TABLE t2 (f11 varchar(1)) ;
+INSERT INTO t2 VALUES ('f'),('d');
+SET @old_optimizer_switch = @@session.optimizer_switch;
+SET SESSION optimizer_switch = 'materialization=on';
+EXPLAIN
+SELECT * FROM t1
+WHERE f3 = (
+SELECT t1.f3 FROM t1
+WHERE ( t1.f10 ) IN ( SELECT f11 FROM t2 GROUP BY f11 ));
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+3	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
+SELECT * FROM t1
+WHERE f3 = (
+SELECT t1.f3 FROM t1
+WHERE ( t1.f10 ) IN ( SELECT f11 FROM t2 GROUP BY f11 ));
+f1	f3	f10
+EXPLAIN
+SELECT * FROM t1
+WHERE f3 = (
+SELECT f3 FROM t1
+WHERE ( f10, f10 ) IN ( SELECT f11, f11 FROM t2 GROUP BY f11 ));
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+2	SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
+3	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	Using temporary; Using filesort
+SELECT * FROM t1
+WHERE f3 = (
+SELECT f3 FROM t1
+WHERE ( f10, f10 ) IN ( SELECT f11, f11 FROM t2 GROUP BY f11 ));
+f1	f3	f10
+SET SESSION optimizer_switch = @old_optimizer_switch;
+drop table t1,t2;

mysql-test/t/subselect4.test

@@ -640,3 +640,38 @@ WHERE EXISTS (
 
 drop table t1,t2;
 
+--echo #
+--echo # LP BUG#718763 Second crash in select_describe() and materialization
+--echo #
+
+CREATE TABLE t1 ( f1 int(11), f3 int(11), f10 varchar(1), KEY (f3)) ;
+INSERT INTO t1 VALUES ('28','6','m'),('29','4','c');
+
+CREATE TABLE t2 (f11 varchar(1)) ;
+INSERT INTO t2 VALUES ('f'),('d');
+
+SET @old_optimizer_switch = @@session.optimizer_switch;
+SET SESSION optimizer_switch = 'materialization=on';
+
+EXPLAIN
+SELECT * FROM t1
+WHERE f3 = (
+        SELECT t1.f3 FROM t1
+        WHERE ( t1.f10 ) IN ( SELECT f11 FROM t2 GROUP BY f11 ));
+SELECT * FROM t1
+WHERE f3 = (
+        SELECT t1.f3 FROM t1
+        WHERE ( t1.f10 ) IN ( SELECT f11 FROM t2 GROUP BY f11 ));
+
+EXPLAIN
+SELECT * FROM t1
+WHERE f3 = (
+        SELECT f3 FROM t1
+        WHERE ( f10, f10 ) IN ( SELECT f11, f11 FROM t2 GROUP BY f11 ));
+SELECT * FROM t1
+WHERE f3 = (
+        SELECT f3 FROM t1
+        WHERE ( f10, f10 ) IN ( SELECT f11, f11 FROM t2 GROUP BY f11 ));
+
+SET SESSION optimizer_switch = @old_optimizer_switch;
+drop table t1,t2;

sql/item_subselect.cc

@@ -1464,8 +1464,15 @@ Item_in_subselect::single_value_transformer(JOIN *join,
 			      (char *)"<no matter>",
 			      (char *)in_left_expr_name);
 
-    master_unit->uncacheable|= UNCACHEABLE_DEPENDENT;
-    //psergey: placed then removed: select_lex->uncacheable|= UNCACHEABLE_DEPENDENT;
+    /*
+      The uncacheable property controls a number of actions, e.g. whether to
+      save/restore (via init_save_join_tab/restore_tmp) the original JOIN for
+      plans with a temp table where the original JOIN was overriden by
+      make_simple_join. The UNCACHEABLE_EXPLAIN is ignored by EXPLAIN, thus
+      non-correlated subqueries will not appear as such to EXPLAIN.
+    */
+    master_unit->uncacheable|= UNCACHEABLE_EXPLAIN;
+    select_lex->uncacheable|= UNCACHEABLE_EXPLAIN;
   }
 
   if (!abort_on_null && left_expr->maybe_null && !pushed_cond_guards)
@@ -1529,6 +1536,9 @@ Item_in_subselect::single_value_in_to_exists_transformer(JOIN * join, Comp_creat
   SELECT_LEX *select_lex= join->select_lex;
   DBUG_ENTER("Item_in_subselect::single_value_in_to_exists_transformer");
 
+  /*
+    The IN=>EXISTS transformation makes non-correlated subqueries correlated.
+  */
   select_lex->uncacheable|= UNCACHEABLE_DEPENDENT;
   if (join->having || select_lex->with_sum_func ||
       select_lex->group_list.elements)
@@ -1742,7 +1752,15 @@ Item_in_subselect::row_value_transformer(JOIN *join)
     optimizer->keep_top_level_cache();
 
     thd->lex->current_select= current;
-    master_unit->uncacheable|= UNCACHEABLE_DEPENDENT;
+    /*
+      The uncacheable property controls a number of actions, e.g. whether to
+      save/restore (via init_save_join_tab/restore_tmp) the original JOIN for
+      plans with a temp table where the original JOIN was overriden by
+      make_simple_join. The UNCACHEABLE_EXPLAIN is ignored by EXPLAIN, thus
+      non-correlated subqueries will not appear as such to EXPLAIN.
+    */
+    master_unit->uncacheable|= UNCACHEABLE_EXPLAIN;
+    select_lex->uncacheable|= UNCACHEABLE_EXPLAIN;
 
     if (!abort_on_null && left_expr->maybe_null && !pushed_cond_guards)
     {
@@ -1796,6 +1814,9 @@ Item_in_subselect::row_value_in_to_exists_transformer(JOIN * join)
 
   DBUG_ENTER("Item_in_subselect::row_value_in_to_exists_transformer");
 
+  /*
+    The IN=>EXISTS transformation makes non-correlated subqueries correlated.
+  */
   select_lex->uncacheable|= UNCACHEABLE_DEPENDENT;
   if (is_having_used)
   {