Comment 1 for bug 628785

Test case:

--disable_warnings
--source include/have_innodb.inc

SET SESSION join_cache_level=9;
SET SESSION optimizer_switch='mrr_sort_keys=off';

CREATE TABLE `D` (
  `pk` int(11) NOT NULL AUTO_INCREMENT,
  `col_int_nokey` int(11) DEFAULT NULL,
  `col_int_key` int(11) DEFAULT NULL,
  `col_varchar_key` varchar(1) DEFAULT NULL,
  `col_varchar_nokey` varchar(1) DEFAULT NULL,
  PRIMARY KEY (`pk`),
  KEY `col_varchar_key` (`col_varchar_key`,`col_int_key`)
) ENGINE=InnoDB AUTO_INCREMENT=101 DEFAULT CHARSET=latin1;
INSERT INTO `D` VALUES (1,6,NULL,'r','r');
INSERT INTO `D` VALUES (2,8,0,'c','c');
INSERT INTO `D` VALUES (97,7,0,'z','z');
INSERT INTO `D` VALUES (98,1,1,'j','j');
INSERT INTO `D` VALUES (99,7,8,'c','c');
INSERT INTO `D` VALUES (100,2,5,'f','f');
SELECT table1 .`col_varchar_key`
FROM D table1 STRAIGHT_JOIN ( D table3 JOIN D table4 ON table4 .`pk` = table3 .`col_int_nokey` ) ON table4 .`col_varchar_nokey` ;