USE test
DROP TABLE IF EXISTS `table1`;
CREATE TABLE `table1` (
  `col1` bigint(20) unsigned NOT NULL ,
  `col2` bigint(20) unsigned NOT NULL ,
  `col3` datetime NOT NULL ,
  PRIMARY KEY (`col3`),
  KEY (`col1`),
  KEY (`col2`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
 PARTITION BY RANGE (TO_DAYS(col3))
(
 PARTITION p_20130310 VALUES LESS THAN (735303) ENGINE = InnoDB,
 PARTITION p_20130311 VALUES LESS THAN (735304) ENGINE = InnoDB,
 PARTITION p_20130312 VALUES LESS THAN (735305) ENGINE = InnoDB
);
INSERT INTO `table1` VALUES (2,96,'2013-03-08 16:28:05');
INSERT INTO `table1` VALUES (1,2,'2013-03-08 16:47:39');
INSERT INTO `table1` VALUES (1,2,'2013-03-08 16:50:27');
INSERT INTO `table1` VALUES (1,2,'2013-03-11 16:33:04');
INSERT INTO `table1` VALUES (1,2,'2013-03-11 16:33:24');
INSERT INTO `table1` VALUES (2,2,'2013-03-12 10:11:48');

SET optimizer_switch='index_merge=on';
SELECT @@optimizer_switch;
SELECT * FROM table1 WHERE col1 = 1 AND col2 = 2
    AND col3 BETWEEN '2013-03-08 00:00:00' AND '2013-03-12 12:00:00'
GROUP BY 1, 2, 3;
EXPLAIN SELECT * FROM table1 WHERE col1 = 1 AND col2 = 2
    AND col3 BETWEEN '2013-03-08 00:00:00' AND '2013-03-12 12:00:00'
GROUP BY 1, 2, 3;

SET optimizer_switch='index_merge=off';
SELECT @@optimizer_switch;
SELECT * FROM table1 WHERE col1 = 1 AND col2 = 2
    AND col3 BETWEEN '2013-03-08 00:00:00' AND '2013-03-12 12:00:00'
GROUP BY 1, 2, 3;
EXPLAIN SELECT * FROM table1 WHERE col1 = 1 AND col2 = 2
    AND col3 BETWEEN '2013-03-08 00:00:00' AND '2013-03-12 12:00:00'
GROUP BY 1, 2, 3;