我有,由于某种原因没有使用任何索引一个相当简单的查询:的Mysql不使用任何索引
CREATE TABLE `events_self` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`date` int(10) unsigned NOT NULL,
`username` varchar(16) CHARACTER SET latin1 COLLATE latin1_general_ci NOT NULL,
`event` enum('status_update','follow_hashtag','make_hashtag','avatar','placeholder_3') CHARACTER SET latin1 COLLATE latin1_general_ci NOT NULL,
`obj_id` varchar(140) CHARACTER SET latin1 COLLATE latin1_general_ci NOT NULL,
`inline` varchar(255) CHARACTER SET latin1 COLLATE latin1_general_ci NOT NULL,
PRIMARY KEY (`id`,`date`),
KEY `obj_id` (`obj_id`),
KEY `user_date` (`username`,`date`),
KEY `event` (`event`),
KEY `x` (`event`,`inline`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
INSERT INTO `events_self` (`id`, `date`, `username`, `event`, `obj_id`, `inline`) VALUES (1, 1358359266, 'aaa', 'make_hashtag', '1', 'scene');
SELECT inline FROM events_self WHERE obj_id = 1;
EXPLAIN SELECT inline FROM events_self WHERE obj_id = 1;
+----+-------------+-------------+------+---------------+------+---------+------+---------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------+------+---------------+------+---------+------+---------+-------------+
| 1 | SIMPLE | events_self | ALL | obj_id | NULL | NULL | NULL | 1610702 | Using where |
+----+-------------+-------------+------+---------------+------+---------+------+---------+-------------+
1 row in set (0.00 sec)
Server版本:5.3.2-MariaDB的-β-mariadb102〜莱尼日志(MariaDB的 - http://mariadb.com/)
我应该离开表/查询原样,还是最好强制使用索引?
这里的问题是?我在您的内容中看不到任何问号 –
这可能是因为对于您的查询,MySQL认为不使用索引是最好的处理方式。试着强制它使用你认为应该的索引并比较结果。 – fge
由于您的表中有一个单一条目,因此,mysql估计执行表扫描时索引会扫描您的查询所需的资源会更少。不要忘记查询执行计划正在考虑表中的行数。 – ioan