如何解决更多奇怪的MySQL行为-查询优化帮助
|| 我们有一个中央登录名，用于支持多个网站。为了存储用户的数据，我们有一个“ 0”表来存储每个用户帐户，然后是每个站点的“ 1”表以获取特定于站点的信息。我们还有一个简单的“ 2”表来存储用户之间的连接。 我们注意到，一个将表连接到主键“ 3”上的查询正在缓慢执行。我希望那里的一些SQL专家可以解释为什么它使用WHERE
mysql> explain select a.username,a.first_name,a.last_name,a.organization_name,a.organization,a.city,a.state,a.zip,a.country,a.profile_photo,a.facebook_id,a.twitter_id,u.reviews from accounts a join users_site1 u ON a.user_id=u.user_id where a.user_id IN (select cid2 from connections where cid1=10001006 AND type=\"MM\" AND status=\"A\") OR a.user_id IN (select cid1 from connections where cid2=10001006 AND type=\"MM\" AND status=\"A\") order by RAND() LIMIT 4;
+----+--------------------+-------------+--------+-------------------+---------+---------+-----------------------+-------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+-------------+--------+-------------------+---------+---------+-----------------------+-------+----------------------------------------------+
| 1 | PRIMARY | u | ALL | PRIMARY | NULL | NULL | NULL | 79783 | Using where; Using temporary; Using filesort |
| 1 | PRIMARY | a | eq_ref | PRIMARY | PRIMARY | 4 | exampledb.u.user_id | 1 | |
| 3 | DEPENDENT SUBQUERY | connections | ref | PRIMARY,cid1,cid2 | cid2 | 6 | const,const | 2 | Using where |
| 2 | DEPENDENT SUBQUERY | connections | ref | PRIMARY,cid2 | cid1 | 6 | const,const | 1 | Using where |
+----+--------------------+-------------+--------+-------------------+---------+---------+-----------------------+-------+----------------------------------------------+
4 rows in set (0.00 sec)
CREATE TABLE `accounts` (
`user_id` int(9) unsigned NOT NULL AUTO_INCREMENT,`username` varchar(40) DEFAULT NULL,`facebook_id` bigint(15) unsigned DEFAULT NULL,`facebook_username` varchar(30) DEFAULT NULL,`password` varchar(20) DEFAULT NULL,`profile_photo` varchar(100) DEFAULT NULL,`first_name` varchar(40) DEFAULT NULL,`middle_name` varchar(40) DEFAULT NULL,`last_name` varchar(40) DEFAULT NULL,`suffix_name` char(3) DEFAULT NULL,`organization_name` varchar(100) DEFAULT NULL,`organization` tinyint(1) unsigned DEFAULT NULL,`address` varchar(200) DEFAULT NULL,`city` varchar(40) DEFAULT NULL,`state` varchar(20) DEFAULT NULL,`zip` varchar(10) DEFAULT NULL,`province` varchar(40) DEFAULT NULL,`country` int(3) DEFAULT NULL,`latitude` decimal(11,7) DEFAULT NULL,`longitude` decimal(12,`phone` varchar(20) DEFAULT NULL,`sex` char(1) DEFAULT NULL,`birthday` date DEFAULT NULL,`about_me` varchar(2000) DEFAULT NULL,`activities` varchar(300) DEFAULT NULL,`website` varchar(100) DEFAULT NULL,`email` varchar(150) DEFAULT NULL,`referrer` int(4) unsigned DEFAULT NULL,`referredid` int(9) unsigned DEFAULT NULL,`verify` int(6) DEFAULT NULL,`status` char(1) DEFAULT \'R\',`created` datetime DEFAULT NULL,`verified` datetime DEFAULT NULL,`activated` datetime DEFAULT NULL,`network` datetime DEFAULT NULL,`deleted` datetime DEFAULT NULL,`logins` int(6) unsigned DEFAULT \'0\',`api_logins` int(6) unsigned DEFAULT \'0\',`last_login` datetime DEFAULT NULL,`last_update` datetime DEFAULT NULL,`private` tinyint(1) unsigned DEFAULT NULL,`ip` varchar(20) DEFAULT NULL,PRIMARY KEY (`user_id`),UNIQUE KEY `username` (`username`),KEY `facebook_id` (`facebook_id`),KEY `status` (`status`),KEY `state` (`state`)
);
CREATE TABLE `users_site1` (
`user_id` int(9) unsigned NOT NULL,`facebook_publish` tinyint(1) unsigned DEFAULT NULL,`facebook_checkin` tinyint(1) unsigned DEFAULT NULL,`facebook_offline` varchar(300) DEFAULT NULL,`twitter_id` varchar(60) DEFAULT NULL,`twitter_secret` varchar(50) DEFAULT NULL,`twitter_username` varchar(20) DEFAULT NULL,`type` char(1) DEFAULT \'M\',`session` varchar(60) DEFAULT NULL,`api_session` varchar(60) DEFAULT NULL,PRIMARY KEY (`user_id`)
);
CREATE TABLE `connections` (
`cid1` int(9) unsigned NOT NULL DEFAULT \'0\',`cid2` int(9) unsigned NOT NULL DEFAULT \'0\',`cid3` int(9) unsigned NOT NULL DEFAULT \'0\',`type` char(2) NOT NULL,`status` char(1) NOT NULL,`updated` datetime DEFAULT NULL,PRIMARY KEY (`cid1`,`cid2`,`type`,`cid3`),KEY `cid1` (`cid1`,`type`),KEY `cid2` (`cid2`,`type`)
);
解决方法
而不是“ 7”，您应该使用另一个联接：
select
a.username,a.first_name,a.last_name,a.organization_name,a.organization,a.city,a.state,a.zip,a.country,a.profile_photo,a.facebook_id,a.twitter_id,u.reviews
from accounts a
join users_site1 u ON a.user_id=u.user_id
join ( select cid2 as id from connections
where cid1=10001006 AND type=\"MM\" AND status=\"A\"
union
select cid1 as id from connections
where cid2=10001006 AND type=\"MM\" AND status=\"A\" ) c
on a.user_id = c.id
order by RAND() LIMIT 4;
order by RAND()
+----+--------------------+-------------+----------------+-------------------+---------+---------+------------------+------+----------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+-------------+----------------+-------------------+---------+---------+------------------+------+----------------------------------------------+
| 1 | PRIMARY | a | ALL | PRIMARY | NULL | NULL | NULL | 2 | Using where; Using temporary; Using filesort |
| 1 | PRIMARY | u | ALL | PRIMARY | NULL | NULL | NULL | 2 | Using where; Using join buffer |
| 3 | DEPENDENT SUBQUERY | connections | index_subquery | PRIMARY,cid1,cid2 | PRIMARY | 14 | func,const,const | 1 | Using where |
| 2 | DEPENDENT SUBQUERY | connections | ref | PRIMARY,cid2 | PRIMARY | 14 | const,func,const | 1 | Using where |
+----+--------------------+-------------+----------------+-------------------+---------+---------+------------------+------+----------------------------------------------+
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