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

.bzrignore

@@ -1433,3 +1433,4 @@ storage/tokudb/ft-index/utils/tokudb_dump
 storage/tokudb/ft-index/utils/tokudb_gen
 storage/tokudb/ft-index/utils/tokudb_load
 libmysql/libmysql_versions.ld
+scripts/mysql_config.pl

mysql-test/r/group_by.result

@@ -2473,3 +2473,12 @@ c	1c
 v	2v,2v
 NULL	1c,2v,2v
 DROP TABLE t1,t2;
+#
+# MDEV-6129: Server crashes during UNION with ORDER BY field IS NULL
+#
+SET sql_mode='ONLY_FULL_GROUP_BY';
+SELECT 1 AS test UNION SELECT 2 AS test ORDER BY test IS NULL ASC;
+test
+1
+2
+SET sql_mode='';

mysql-test/t/group_by.test

@@ -1643,3 +1643,14 @@ FROM t1 JOIN t2 ON c = b GROUP BY b WITH ROLLUP;
 
 DROP TABLE t1,t2;
 
+--echo #
+--echo # MDEV-6129: Server crashes during UNION with ORDER BY field IS NULL
+--echo #
+
+SET sql_mode='ONLY_FULL_GROUP_BY';
+SELECT 1 AS test UNION SELECT 2 AS test ORDER BY test IS NULL ASC;
+SET sql_mode='';
+
+#
+# End of MariaDB 5.5 tests
+#

sql/db.opt

-default-character-set=latin1
-default-collation=latin1_swedish_ci

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