Fixed bug #20869.

The bug caused a crash of the server if a subquery with
ORDER BY DESC used the range access method.
The bug happened because the method QUICK_SELECT_DESC::reset
was not reworked after MRR interface had been introduced.

mysql-test/r/subselect.result

@@ -3238,3 +3238,39 @@ i
 10000000000000000000
 DROP TABLE t1;
 DROP TABLE t2;
+CREATE TABLE t1 (
+i1 int(11) NOT NULL default '0',
+i2 int(11) NOT NULL default '0',
+t datetime NOT NULL default '0000-00-00 00:00:00',
+PRIMARY KEY  (i1,i2,t)
+);
+INSERT INTO t1 VALUES 
+(24,1,'2005-03-03 16:31:31'),(24,1,'2005-05-27 12:40:07'),
+(24,1,'2005-05-27 12:40:08'),(24,1,'2005-05-27 12:40:10'),
+(24,1,'2005-05-27 12:40:25'),(24,1,'2005-05-27 12:40:30'),
+(24,2,'2005-03-03 13:43:05'),(24,2,'2005-03-03 16:23:31'),
+(24,2,'2005-03-03 16:31:30'),(24,2,'2005-05-27 12:37:02'),
+(24,2,'2005-05-27 12:40:06');
+CREATE TABLE t2 (
+i1 int(11) NOT NULL default '0',
+i2 int(11) NOT NULL default '0',
+t datetime default NULL,
+PRIMARY KEY  (i1)
+);
+INSERT INTO t2 VALUES (24,1,'2006-06-20 12:29:40');
+EXPLAIN
+SELECT * FROM t1,t2
+WHERE t1.t = (SELECT t1.t FROM t1 
+WHERE t1.t < t2.t  AND t1.i2=1 AND t2.i1=t1.i1
+ORDER BY t1.t DESC LIMIT 1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t2	system	NULL	NULL	NULL	NULL	1	
+1	PRIMARY	t1	index	NULL	PRIMARY	16	NULL	11	Using where; Using index
+2	DEPENDENT SUBQUERY	t1	range	PRIMARY	PRIMARY	16	NULL	5	Using where; Using index
+SELECT * FROM t1,t2
+WHERE t1.t = (SELECT t1.t FROM t1 
+WHERE t1.t < t2.t  AND t1.i2=1 AND t2.i1=t1.i1
+ORDER BY t1.t DESC LIMIT 1);
+i1	i2	t	i1	i2	t
+24	1	2005-05-27 12:40:30	24	1	2006-06-20 12:29:40
+DROP TABLE t1, t2;

mysql-test/t/subselect.test

@@ -2161,3 +2161,41 @@ SELECT t1.i FROM t1 WHERE t1.i = CAST((SELECT MAX(i) FROM t2) AS UNSIGNED);
 
 DROP TABLE t1;
 DROP TABLE t2;
+
+# 
+# Bug#20869: subselect with range access by DESC
+#
+
+CREATE TABLE t1 (
+  i1 int(11) NOT NULL default '0',
+  i2 int(11) NOT NULL default '0',
+  t datetime NOT NULL default '0000-00-00 00:00:00',
+  PRIMARY KEY  (i1,i2,t)
+);
+INSERT INTO t1 VALUES 
+(24,1,'2005-03-03 16:31:31'),(24,1,'2005-05-27 12:40:07'),
+(24,1,'2005-05-27 12:40:08'),(24,1,'2005-05-27 12:40:10'),
+(24,1,'2005-05-27 12:40:25'),(24,1,'2005-05-27 12:40:30'),
+(24,2,'2005-03-03 13:43:05'),(24,2,'2005-03-03 16:23:31'),
+(24,2,'2005-03-03 16:31:30'),(24,2,'2005-05-27 12:37:02'),
+(24,2,'2005-05-27 12:40:06');
+
+CREATE TABLE t2 (
+  i1 int(11) NOT NULL default '0',
+  i2 int(11) NOT NULL default '0',
+  t datetime default NULL,
+  PRIMARY KEY  (i1)
+);
+INSERT INTO t2 VALUES (24,1,'2006-06-20 12:29:40');
+
+EXPLAIN
+SELECT * FROM t1,t2
+  WHERE t1.t = (SELECT t1.t FROM t1 
+                  WHERE t1.t < t2.t  AND t1.i2=1 AND t2.i1=t1.i1
+                    ORDER BY t1.t DESC LIMIT 1);
+SELECT * FROM t1,t2
+  WHERE t1.t = (SELECT t1.t FROM t1 
+                  WHERE t1.t < t2.t  AND t1.i2=1 AND t2.i1=t1.i1
+                    ORDER BY t1.t DESC LIMIT 1);
+
+DROP TABLE t1, t2;

sql/opt_range.h

@@ -668,7 +668,7 @@ private:
 #ifdef NOT_USED
   bool test_if_null_range(QUICK_RANGE *range, uint used_key_parts);
 #endif
-  int reset(void) { next=0; rev_it.rewind(); return 0; }
+  int reset(void) { rev_it.rewind(); return QUICK_RANGE_SELECT::reset(); }
   List<QUICK_RANGE> rev_ranges;
   List_iterator<QUICK_RANGE> rev_it;
 };