小编use*_*742的帖子

这是我的完整查询:

SELECT * FROM `clientgroupassign`
LEFT JOIN `clients` ON `clientgroupassign`.clientId = `clients`.clientId
LEFT JOIN `users` ON `carerId` = `userId`
LEFT JOIN 
    (SELECT * FROM 
        (SELECT * FROM `contacts` WHERE `contactGroup` = 4 ORDER BY `contactId` DESC) 
        as `contacts` 
    GROUP BY (`contactClientId`)
    )  AS `contacts` ON `contactClientId` = `clients`.clientId
WHERE groupId = 4
ORDER BY `clients`.clientId

第三次连接存在问题导致脚本执行约1分钟.当我在PMA中分开运行时:

SELECT * FROM (SELECT * FROM `contacts` WHERE `contactGroup` = 4 ORDER BY `contactId` DESC) AS `contacts` GROUP BY (`contactClientId`)

执行仍然很长.

我想要的是为contacts第4组中的每个客户端添加一个,最后添加的行(客户端可以在不同的组中). …