Suposse我有下一个拥有500.000行的MySQL数据库：
users
{
id - int,name - varchar(32),verified - tinyint(1)
}
primary { id }
index { verified }
SELECT * FROM users WHERE verified != 1 ORDER BY id DESC LIMIT 20
但它需要1.2秒才能完成.
我该如何优化它？或者在PHP中以其他方式获得相同的结果.
[编辑]
ID是主索引,VERIFIED也是索引
[编辑2]
CREATE TABLE `users` (
`id` int(10) unsigned NOT NULL auto_increment COMMENT 'Identificador del usuario',`login` varchar(32) NOT NULL COMMENT 'Login para entrar',`password` varchar(32) NOT NULL COMMENT 'Password para entrar',`email` varchar(384) NOT NULL COMMENT 'Email del usuario',`group_id` int(10) unsigned default NULL,`display_name` varchar(64) NOT NULL COMMENT 'Nombre para mostrar',`email_verified` tinyint(3) unsigned default '0' COMMENT 'Email verificado?',`banned` tinyint(3) unsigned default '0' COMMENT 'Baneado?',`admin` tinyint(3) unsigned default '0' COMMENT 'Es un super administrador del sitio?',`registered` int(10) unsigned NOT NULL COMMENT 'Fecha del registro',PRIMARY KEY (`id`),KEY `login` (`login`),KEY `password` (`password`),KEY `email` (`email`(333)),KEY `group_id` (`group_id`),KEY `email_verified` (`email_verified`),KEY `banned` (`banned`),KEY `admin` (`admin`),KEY `registered` (`registered`)
) ENGINE=MyISAM AUTO_INCREMENT=500002 DEFAULT CHARSET=utf8;
[编辑3]
EXPLAIN(SELECT id FROM users WHERE email_verified != 1 ORDER BY id DESC LIMIT 20)
是
id: 1
select_type: SIMPLE
table: users
type: range
possible_keys: email_verified
key: email_verified
key_len: 2
ref:
rows: 345195
Extra: Using where; Using filesort
以及查询的个人资料：
Status Duration
(initialization) 0.0000307
opening tables 0.000003
System lock 0.0000017
Table lock 0.0000042
init 0.000017
optimizing 0.0000077
statistics 0.000097
preparing 0.000054
executing 0.0000007
Sorting result 1.2321507
Sending data 0.000272
end 0.000004
query end 0.0000025
freeing items 0.0000099
closing tables 0.0000025
logging slow query 0.0000005
最佳答案
您需要一个包含id和email_verfied的索引
KEY `foo` (`id`,`email_verified`)
然后打开EXPLAIN(SELECT id FROM users WHERE email_verified！= 1 ORDER BY id DESC LIMIT 20)
+----+-------------+-------+-------+----------------+---------+---------+------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------+----------------+---------+---------+------+------+--------------------------+
| 1 | SIMPLE | users | index | email_verified | Index 4 | 6 | NULL | 5 | Using where; Using index |
+----+-------------+-------+-------+----------------+---------+---------+------+------+--------------------------+
特别是慢速使用filesort已经消失了.