MDEV-6129: Server crashes during UNION with ORDER BY field IS NULL

Fixed crashing bug for union queries where there was no real tables.


mysql-test/r/group_by.result:
  Added test case
mysql-test/t/group_by.test:
  Added test case
sql/db.opt:
  Removed genrated file
sql/item.cc:
  Handled case when table_list->pos_in_tables is not set. Can only happens when there is no real tables in query

1 files changed, 15 insertions, 7 deletions

diff --git a/sql/item.cc b/sql/item.cc
index a4ab81a9e5a..b3d4b4a7616 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -5273,15 +5273,23 @@ mark_non_agg_field:
     /*
       Mark selects according to presence of non aggregated fields.
       Fields from outer selects added to the aggregate function
-      outer_fields list as its unknown at the moment whether it's
+      outer_fields list as it's unknown at the moment whether it's
       aggregated or not.
-      We're using either the select lex of the cached table (if present)
-      or the field's resolution context. context->select_lex is 
-      safe for use because it's either the SELECT we want to use 
-      (the current level) or a stub added by non-SELECT queries.
+      We're using the select lex of the cached table (if present).
     */
-    SELECT_LEX *select_lex= cached_table ? 
-      cached_table->select_lex : field->table->pos_in_table_list->select_lex;
+    SELECT_LEX *select_lex;
+    if (cached_table)
+      select_lex= cached_table->select_lex;
+    else if (!(select_lex= field->table->pos_in_table_list->select_lex))
+    {
+      /*
+        This can only happen when there is no real table in the query.
+        We are using the field's resolution context. context->select_lex is eee
+        safe for use because it's either the SELECT we want to use 
+        (the current level) or a stub added by non-SELECT queries.
+      */
+      select_lex= context->select_lex;
+    }
     if (!thd->lex->in_sum_func)
       select_lex->set_non_agg_field_used(true);
     else