Fixed bug mdev-5091.

The function SELECT_LEX::update_used_tables should process all
ORDER BY lists in any subselect of a union.

mysql-test/r/union.result

@@ -1724,3 +1724,18 @@ foo
 1
 deallocate prepare stmt1;
 End of 5.1 tests
+#
+# mdev-5091: Asseirtion failure for UNION with ORDER BY 
+#            in one of selects
+#
+CREATE TABLE t1 (i int, c char(1)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (6,'b');
+CREATE VIEW v1 AS SELECT * FROM t1;
+( SELECT i FROM v1 GROUP BY i ORDER BY CONCAT( c, c ) LIMIT 1 )
+UNION 
+( SELECT i FROM t1 );
+i
+6
+DROP VIEW v1;
+DROP TABLE t1;
+End of 5.3 tests

mysql-test/t/union.test

@@ -1210,3 +1210,22 @@ execute stmt1;
 deallocate prepare stmt1;
 
 --echo End of 5.1 tests
+--echo #
+--echo # mdev-5091: Asseirtion failure for UNION with ORDER BY 
+--echo #            in one of selects
+--echo #
+ 
+ CREATE TABLE t1 (i int, c char(1)) ENGINE=MyISAM;
+ INSERT INTO t1 VALUES (6,'b');
+
+ CREATE VIEW v1 AS SELECT * FROM t1;
+
+ ( SELECT i FROM v1 GROUP BY i ORDER BY CONCAT( c, c ) LIMIT 1 )
+ UNION 
+ ( SELECT i FROM t1 );
+
+ DROP VIEW v1;
+ DROP TABLE t1;
+
+ --echo End of 5.3 tests
+

sql/sql_lex.cc

@@ -3534,7 +3534,7 @@ void SELECT_LEX::update_used_tables()
   }
   for (ORDER *order= group_list.first; order; order= order->next)
     (*order->item)->update_used_tables();
-  if (!master_unit()->is_union())
+  if (master_unit()->global_parameters != this)
   {
     for (ORDER *order= order_list.first; order; order= order->next)
       (*order->item)->update_used_tables();