[英]Mysql subquery optimization - count
i have these subqueries in a main query used to fetch some events: 我在用于获取某些事件的主查询中有这些子查询:
SELECT [...],
(SELECT COUNT(*) FROM WEventUser WHERE WEventUser.eID=e.eID AND favorited=1) as numfavorited,
(SELECT COUNT(*) FROM WEventUser WHERE WEventUser.eID=e.eID AND subscribed=1) as numsubscribed,
(SELECT COUNT(*) FROM WEventUser WHERE eID=e.eID AND WEventUser.uID=2 AND favorited=1) as favorited,
(SELECT COUNT(*) FROM WEventUser WHERE eID=e.eID AND WEventUser.uID=2 AND subscribed=1) as subscribed,
[...] WHERE...etc.
structure of WEventUser is quite simple WEventUser的结构非常简单
CREATE TABLE IF NOT EXISTS `WEventUser` (
`eID` int(10) unsigned NOT NULL auto_increment,
`uID` int(10) unsigned NOT NULL,
`favorited` int(1) unsigned default '0',
`subscribed` int(1) unsigned default '0',
PRIMARY KEY (`eID`,`uID`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
These subqueries are really expensive. 这些子查询非常昂贵。 Can you help me finding an alternative (like a single join)?
你能帮我找一个替代方案(比如一个连接)吗?
Thanks in advance! 提前致谢!
EDIT: I'm selecting from a main WEvents table that is: 编辑:我从一个主要的WEvents表中选择:
CREATE TABLE IF NOT EXISTS `wevents` (
`eID` int(10) unsigned NOT NULL AUTO_INCREMENT,
`uID` int(10) unsigned DEFAULT NULL,
`ecID` int(10) unsigned NOT NULL,
`eName` varchar(64) NOT NULL,
`eDescription` longtext,
`eIsActive` varchar(1) NOT NULL DEFAULT '0',
`eIsValidated` tinyint(4) NOT NULL DEFAULT '-1',
`eDateAdded` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
`eDateModified` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
PRIMARY KEY (`eID`,`ecID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
You shouldn't use a subqueries, it is enough to count values in the COUNT function, eg - 你不应该使用子查询,它足以计算COUNT函数中的值,例如 -
SELECT [...],
COUNT(IF(wu.favorited = 1, 1, NULL)) as numfavorited,
COUNT(IF(wu.subscribed = 1, 1, NULL)) as numsubscribed,
COUNT(IF(wu.uID=2 AND wu.favorited=1, 1, NULL)) as favorited,
COUNT(IF(wu.uID=2 AND wu.favorited = 1, 1, NULL)) as subscribed,
[...]
FROM
WEventUser wu
WHERE...etc.
You can easily use this one if you want to join WEventUser
with another table. 如果要将
WEventUser
与另一个表连接,可以轻松使用此方法。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.