Fixed bug mdev-10875.

Now, after the implementation of mdev-8646
"Re-engineer the code for post-join operations"
create_sort_index() can be called for subqueries.

mysql-test/r/win.result

@@ -2382,3 +2382,19 @@ pk	c	CNT
 10	2	0.5000
 drop view v1,v2,v3,v4;
 drop table t0,t1;
+#
+# MDEV-10875: window function in subquery
+#
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES (3),(1);
+CREATE TABLE t2 (c VARCHAR(8));
+INSERT INTO t2 VALUES ('foo'),('bar'),('foo');
+SELECT COUNT(*) OVER (PARTITION BY c) FROM t2;
+COUNT(*) OVER (PARTITION BY c)
+2
+1
+2
+SELECT * FROM t1 WHERE i IN ( SELECT COUNT(*) OVER (PARTITION BY c) FROM t2 );
+i
+1
+DROP TABLE t1, t2;

mysql-test/t/win.test

@@ -1426,3 +1426,19 @@ select * from v4;
 
 drop view v1,v2,v3,v4;
 drop table t0,t1;
+
+--echo #
+--echo # MDEV-10875: window function in subquery
+--echo #
+
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES (3),(1);
+
+CREATE TABLE t2 (c VARCHAR(8));
+INSERT INTO t2 VALUES ('foo'),('bar'),('foo');
+
+SELECT COUNT(*) OVER (PARTITION BY c) FROM t2;
+
+SELECT * FROM t1 WHERE i IN ( SELECT COUNT(*) OVER (PARTITION BY c) FROM t2 );
+
+DROP TABLE t1, t2;

sql/sql_select.cc

@@ -21403,9 +21403,6 @@ create_sort_index(THD *thd, JOIN *join, JOIN_TAB *tab, Filesort *fsort)
   table=  tab->table;
   select= fsort->select;
  
-  /* Currently ORDER BY ... LIMIT is not supported in subqueries. */
-  DBUG_ASSERT(join->group_list || !join->is_in_subquery());
-
   table->status=0;				// May be wrong if quick_select
 
   if (!tab->preread_init_done && tab->preread_init())