MDEV-9513: Assertion `join->group_list || !join->is_in_subquery()' failed in create_sort_index

Removing the ORDER BY clause from the UNION when UNION is inside an IN/ALL/ANY/EXISTS subquery.
The rewrites are done for subqueries but this rewrite is not done for the fake_select of
the UNION.

1 files changed, 19 insertions, 0 deletions

diff --git a/sql/sql_union.cc b/sql/sql_union.cc
index 38de2d592ed..0e623777ef0 100644
--- a/sql/sql_union.cc
+++ b/sql/sql_union.cc
@@ -388,6 +388,25 @@ bool st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
   found_rows_for_union= first_sl->options & OPTION_FOUND_ROWS;
   is_union_select= is_union() || fake_select_lex;
 
+  /*
+    If we are reading UNION output and the UNION is in the
+    IN/ANY/ALL/EXISTS subquery, then ORDER BY is redundant and hence should
+    be removed.
+    Example:
+     select ... col IN (select col2 FROM t1 union select col3 from t2 ORDER BY 1)
+
+    (as for ORDER BY ... LIMIT, it currently not supported inside
+     IN/ALL/ANY subqueries)
+    (For non-UNION this removal of ORDER BY clause is done in
+     check_and_do_in_subquery_rewrites())
+  */
+  if (is_union() && item &&
+      (item->is_in_predicate() || item->is_exists_predicate()))
+  {
+    global_parameters()->order_list.first= NULL;
+    global_parameters()->order_list.elements= 0;
+  }
+
   /* Global option */
 
   if (is_union_select)