Question

I have a rather simple query that for some reason is not using any index:

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 version: 5.3.2-MariaDB-beta-mariadb102~lenny-log (MariaDB – http://mariadb.com/)

Should I leave the table / query as is or it would be best to force the use of an index?

Answer 1

try this

EXPLAIN SELECT inline FROM events_self  WHERE obj_id = "1";

Since you sent the integer, MySql will not consider the indexing as type is different.