merge

mysql-test/r/order_by.result

@@ -1463,6 +1463,15 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c;
 col
 1
+# Must use ref-or-null on the a_c index
+EXPLAIN
+SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c DESC;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	ref_or_null	a_c,a	x	x	x	x	x
+# Must return 1 row
+SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c DESC;
+col
+1
 DROP TABLE t1;
 End of 5.0 tests
 CREATE TABLE t2 (a varchar(32), b int(11), c float, d double, 

mysql-test/t/order_by.test

@@ -886,6 +886,15 @@ SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c;
 --echo # Must return 1 row
 SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c;
 
+# part 2 of the problem : DESC test cases
+--echo # Must use ref-or-null on the a_c index
+--replace_column 1 x 2 x 3 x 6 x 7 x 8 x 9 x 10 x
+EXPLAIN
+SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c DESC;
+--echo # Must return 1 row
+SELECT 1 AS col FROM t1 WHERE a=2 AND (c=10 OR c IS NULL) ORDER BY c DESC;
+
+
 DROP TABLE t1;
 
 

sql/sql_select.cc

@@ -13487,7 +13487,7 @@ check_reverse_order:
 	select->quick=tmp;
       }
     }
-    else if (tab->type != JT_NEXT && 
+    else if (tab->type != JT_NEXT && tab->type != JT_REF_OR_NULL &&
              tab->ref.key >= 0 && tab->ref.key_parts <= used_key_parts)
     {
       /*