Merge 10.4 into 10.5

1 files changed, 21 insertions, 1 deletions

diff --git a/sql/sql_union.cc b/sql/sql_union.cc
index 3360c3c18cb..f1df76508d7 100644
--- a/sql/sql_union.cc
+++ b/sql/sql_union.cc
@@ -1,5 +1,5 @@
 /* Copyright (c) 2000, 2017, Oracle and/or its affiliates.
-   Copyright (c) 2010, 2017, Corporation
+   Copyright (c) 2010, 2020, MariaDB Corporation.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -1364,6 +1364,25 @@ bool st_select_lex_unit::prepare(TABLE_LIST *derived_arg,
   found_rows_for_union= first_sl->options & OPTION_FOUND_ROWS;
   is_union_select= is_unit_op() || fake_select_lex || single_tvc;
 
+  /*
+    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 (item && is_unit_op() &&
+      (item->is_in_predicate() || item->is_exists_predicate()))
+  {
+    global_parameters()->order_list.first= NULL;
+    global_parameters()->order_list.elements= 0;
+  }
+
   /* will only optimize once */
   if (!bag_set_op_optimized && !is_recursive)
   {
@@ -1390,6 +1409,7 @@ bool st_select_lex_unit::prepare(TABLE_LIST *derived_arg,
       break;
     }
   }
+
   /* Global option */
 
   if (is_union_select || is_recursive)