MDEV-15208: server crashed, when using ORDER BY with window function and UNION

SELECTs inside a UNION can have window function but not the global ORDER BY clause of the UNION.

mysql-test/r/win.result

@@ -4230,5 +4230,13 @@ i	LAST_VALUE(COUNT(i)) OVER (PARTITION BY i ORDER BY j)
 4	2
 DROP TABLE t1;
 #
+# MDEV-15208: server crashed, when using ORDER BY with window function and UNION
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(1),(1),(1),(1),(2),(2),(2),(2),(2),(2);
+SELECT 1 UNION SELECT a FROM t1 ORDER BY (row_number() over ());
+ERROR HY000: Expression #1 of ORDER BY contains aggregate function and applies to a UNION
+DROP TABLE t1;
+#
 # End of 10.2 tests
 #

mysql-test/t/win.test

@@ -2730,6 +2730,16 @@ INSERT INTO t1 VALUES (1,1), (1,5),(1,4), (2,2),(2,5), (3,3),(4,4);
 SELECT i, LAST_VALUE(COUNT(i)) OVER (PARTITION BY i ORDER BY j) FROM t1 GROUP BY i;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-15208: server crashed, when using ORDER BY with window function and UNION
+--echo #
+
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(1),(1),(1),(1),(2),(2),(2),(2),(2),(2);
+--error ER_AGGREGATE_ORDER_FOR_UNION
+SELECT 1 UNION SELECT a FROM t1 ORDER BY (row_number() over ());
+DROP TABLE t1;
+
 --echo #
 --echo # End of 10.2 tests
 --echo #

sql/sql_select.cc

@@ -22796,7 +22796,9 @@ int setup_order(THD *thd, Ref_ptr_array ref_pointer_array, TABLE_LIST *tables,
       an ORDER BY clause
     */
 
-    if (for_union && (*order->item)->with_sum_func)
+    if (for_union &&
+        ((*order->item)->with_sum_func ||
+         (*order->item)->with_window_func))
     {
       my_error(ER_AGGREGATE_ORDER_FOR_UNION, MYF(0), number);
       return 1;