No other way than delete primary key to create partitions by single datetime columns?

[Sam Young]

Hi, I have a question, the table like this

CREATE TABLE `t1` (
`id` varchar(64) NOT NULL,
`createDate` datetime DEFAULT NULL,
`col3` int(11) DEFAULT NULL,
`col4` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

The table is so huge that I want partition it by `createDate` column to have a better select performance.

Partition like this:

ALTER TABLE t1 PARTITION BY RANGE COLUMNS (createDate)(
PARTITION p2015_6_1 VALUES less than ('2015-6-1'),
PARTITION p2015_7_1 VALUES less than ('2015-7-1'),
PARTITION pmax VALUES LESS THAN (MAXVALUE)
);

Is this no other way than delete primary key ?
Or some trick usage that partition it by a range column and keep the primary key ?