Mysql的子查詢優化 - 計數

Question

我有用來獲取一些事件主查詢，這些子查詢：

WEventUser的

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. 

結構相當簡單

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; 

這些子查詢是真的很貴。你能幫我找到一個替代方案嗎？

在此先感謝！

編輯： 我從主WEvents表即選擇：

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; 

Answer 1

你不應該使用一個子查詢，這是不夠的COUNT函數計算的值，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. 

，如果你想加入WEventUser與另一個表可以很容易地使用這一個。