CREATE TABLE `tmp_xf_like` (

  `id` int(11) NOT NULL AUTO_INCREMENT,

  `user_id` bigint(20) NOT NULL,

  `title` varchar(128) NOT NULL,

  `memo` varchar(2000) DEFAULT NULL,

  PRIMARY KEY (`id`),

  KEY `idx_userid` (`title`),

  KEY `user_id` (`user_id`)

) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

mysql> explain select id from tmp_xf_like where title='a';

+----+-------------+-------------+------+---------------+------------+---------+-------+------+--------------------------+

| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |

+----+-------------+-------------+------+---------------+------------+---------+-------+------+--------------------------+

| 1 | SIMPLE | tmp_xf_like | ref | idx_userid | idx_userid | 386 | const | 1 | Using where; Using index |

+----+-------------+-------------+------+---------------+------------+---------+-------+------+--------------------------+

1 row in set (0.01 sec)

explain select id from tmp_xf_like where user_id=1;

+----+-------------+-------------+------+---------------+---------+---------+-------+------+-------------+

| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |

+----+-------------+-------------+------+---------------+---------+---------+-------+------+-------------+

| 1 | SIMPLE | tmp_xf_like | ref | user_id | user_id | 8 | const | 1 | Using index |

+----+-------------+-------------+------+---------------+---------+---------+-------+------+-------------+

1 row in set (0.00 sec)