Test case:

--disable_warnings
DROP TABLE /*! IF EXISTS */ CC;
DROP TABLE /*! IF EXISTS */ C;
--enable_warnings

CREATE TABLE `CC` (
  `pk` int(11) NOT NULL AUTO_INCREMENT,
  `col_int_nokey` int(11) DEFAULT NULL,
  `col_int_key` int(11) DEFAULT NULL,
  `col_time_key` time DEFAULT NULL,
  `col_varchar_key` varchar(1) DEFAULT NULL,
  `col_varchar_nokey` varchar(1) DEFAULT NULL,
  PRIMARY KEY (`pk`),
  KEY `col_int_key` (`col_int_key`),
  KEY `col_time_key` (`col_time_key`),
  KEY `col_varchar_key` (`col_varchar_key`,`col_int_key`)
) ENGINE=MyISAM AUTO_INCREMENT=30 DEFAULT CHARSET=latin1;
INSERT INTO `CC` VALUES (10,7,8,'01:27:35','v','v');
INSERT INTO `CC` VALUES (11,1,9,'19:48:31','r','r');
INSERT INTO `CC` VALUES (12,5,9,'00:00:00','a','a');
INSERT INTO `CC` VALUES (13,3,186,'19:53:05','m','m');
INSERT INTO `CC` VALUES (14,6,NULL,'19:18:56','y','y');
INSERT INTO `CC` VALUES (15,92,2,'10:55:12','j','j');
INSERT INTO `CC` VALUES (16,7,3,'00:25:00','d','d');
INSERT INTO `CC` VALUES (17,NULL,0,'12:35:47','z','z');
INSERT INTO `CC` VALUES (18,3,133,'19:53:03','e','e');
INSERT INTO `CC` VALUES (19,5,1,'17:53:30','h','h');
INSERT INTO `CC` VALUES (20,1,8,'11:35:49','b','b');
INSERT INTO `CC` VALUES (21,2,5,NULL,'s','s');
INSERT INTO `CC` VALUES (22,NULL,5,'06:01:40','e','e');
INSERT INTO `CC` VALUES (23,1,8,'05:45:11','j','j');
INSERT INTO `CC` VALUES (24,0,6,'00:00:00','e','e');
INSERT INTO `CC` VALUES (25,210,51,'00:00:00','f','f');
INSERT INTO `CC` VALUES (26,8,4,'06:11:01','v','v');
INSERT INTO `CC` VALUES (27,7,7,'13:02:46','x','x');
INSERT INTO `CC` VALUES (28,5,6,'21:44:25','m','m');
INSERT INTO `CC` VALUES (29,NULL,4,'22:43:58','c','c');
CREATE TABLE `C` (
  `pk` int(11) NOT NULL AUTO_INCREMENT,
  `col_int_nokey` int(11) DEFAULT NULL,
  `col_int_key` int(11) DEFAULT NULL,
  `col_time_key` time DEFAULT NULL,
  `col_varchar_key` varchar(1) DEFAULT NULL,
  `col_varchar_nokey` varchar(1) DEFAULT NULL,
  PRIMARY KEY (`pk`),
  KEY `col_int_key` (`col_int_key`),
  KEY `col_time_key` (`col_time_key`),
  KEY `col_varchar_key` (`col_varchar_key`,`col_int_key`)
) ENGINE=MyISAM AUTO_INCREMENT=21 DEFAULT CHARSET=latin1;
INSERT INTO `C` VALUES (1,NULL,2,'11:28:45','w','w');
INSERT INTO `C` VALUES (2,7,9,'20:25:14','m','m');
INSERT INTO `C` VALUES (3,9,3,'13:47:24','m','m');
INSERT INTO `C` VALUES (4,7,9,'19:24:11','k','k');
INSERT INTO `C` VALUES (5,4,NULL,'15:59:13','r','r');
INSERT INTO `C` VALUES (6,2,9,'00:00:00','t','t');
INSERT INTO `C` VALUES (7,6,3,'15:15:04','j','j');
INSERT INTO `C` VALUES (8,8,8,'11:32:06','u','u');
INSERT INTO `C` VALUES (9,NULL,8,'18:32:33','h','h');
INSERT INTO `C` VALUES (10,5,53,'15:19:25','o','o');
INSERT INTO `C` VALUES (11,NULL,0,'19:03:19',NULL,NULL);
INSERT INTO `C` VALUES (12,6,5,'00:39:46','k','k');
INSERT INTO `C` VALUES (13,188,166,NULL,'e','e');
INSERT INTO `C` VALUES (14,2,3,'00:00:00','n','n');
INSERT INTO `C` VALUES (15,1,0,'13:12:11','t','t');
INSERT INTO `C` VALUES (16,1,1,'04:56:48','c','c');
INSERT INTO `C` VALUES (17,0,9,'19:56:05','m','m');
INSERT INTO `C` VALUES (18,9,5,'19:35:19','y','y');
INSERT INTO `C` VALUES (19,NULL,6,'05:03:03','f','f');
INSERT INTO `C` VALUES (20,4,2,'18:38:59','d','d');



set @@optimizer_switch='subquery_cache=off';

/* cache is off */ SELECT     (
SELECT 4
FROM DUAL ) AS field1 , SUM( DISTINCT table1 . `pk` ) AS field2 ,  (
SELECT   MAX(  SUBQUERY2_t1 . `col_int_nokey` ) AS SUBQUERY2_field1
FROM ( C AS SUBQUERY2_t1 INNER JOIN C AS SUBQUERY2_t2 ON (SUBQUERY2_t2 . `col_int_key` = SUBQUERY2_t1 . `pk`  ) )
WHERE SUBQUERY2_t2 . `col_varchar_nokey` <= table1 . `col_varchar_key` OR SUBQUERY2_t1 . `col_int_nokey` < table1 . `pk` ) AS field3 , table1 . `col_time_key` AS field4 , table1 . `col_int_key` AS field5 , CONCAT ( table2 . `col_varchar_nokey` , table1 . `col_varchar_key` ) AS field6
FROM ( C AS table1 INNER JOIN ( ( C AS table2 LEFT JOIN CC AS table3 ON (table3 . `col_varchar_key` = table2 . `col_varchar_key`  ) ) ) ON (table3 . `col_varchar_key` = table2 . `col_varchar_nokey`  ) )
WHERE (  table2 . `col_varchar_nokey` NOT IN (
SELECT 'd' UNION
SELECT 'u' ) ) OR table3 . `col_varchar_nokey` <= table1 . `col_varchar_key`
GROUP BY field1, field3, field4, field5, field6
ORDER BY table1 . `col_int_key`  , field1, field2, field3, field4, field5, field6
;

set @@optimizer_switch='subquery_cache=on';

/* cache is on */ SELECT     (
SELECT 4
FROM DUAL ) AS field1 , SUM( DISTINCT table1 . `pk` ) AS field2 ,  (
SELECT   MAX(  SUBQUERY2_t1 . `col_int_nokey` ) AS SUBQUERY2_field1
FROM ( C AS SUBQUERY2_t1 INNER JOIN C AS SUBQUERY2_t2 ON (SUBQUERY2_t2 . `col_int_key` = SUBQUERY2_t1 . `pk`  ) )
WHERE SUBQUERY2_t2 . `col_varchar_nokey` <= table1 . `col_varchar_key` OR SUBQUERY2_t1 . `col_int_nokey` < table1 . `pk` ) AS field3 , table1 . `col_time_key` AS field4 , table1 . `col_int_key` AS field5 , CONCAT ( table2 . `col_varchar_nokey` , table1 . `col_varchar_key` ) AS field6
FROM ( C AS table1 INNER JOIN ( ( C AS table2 LEFT JOIN CC AS table3 ON (table3 . `col_varchar_key` = table2 . `col_varchar_key`  ) ) ) ON (table3 . `col_varchar_key` = table2 . `col_varchar_nokey`  ) )
WHERE (  table2 . `col_varchar_nokey` NOT IN (
SELECT 'd' UNION
SELECT 'u' ) ) OR table3 . `col_varchar_nokey` <= table1 . `col_varchar_key`
GROUP BY field1, field3, field4, field5, field6
ORDER BY table1 . `col_int_key`  , field1, field2, field3, field4, field5, field6
;