SQL在LEFT JOIN上获取最大id字段

Question

我试图从tblimage中拉出与每个用户的tblimage中的maxid相对应的照片.目前,我收到消息表中的所有消息和发布消息的用户的随机照片,我希望照片是最新上传的照片.它现在写的方式只是从表中拉出一张随机照片.有什么建议？

表结构如下:

消息:msgstr,message,user_id,event_id
tblimage:id,photo,userid

SELECT messages.*, tblimage.photo, max(tblimage.id) 
        FROM messages LEFT JOIN tblimage ON messages.user_id = tblimage.userid 
        GROUP BY messages.msg_id, messages.user_id 
        ORDER BY messages.msg_id DESC, tblimage.id desc

Answer 1

尝试

SELECT messages.*, T2.photo
FROM messages
LEFT JOIN (SELECT userid, MAX(id) AS maxid
           FROM tblimages
           GROUP BY userid) AS T1
ON messages.user_id = T1.userid
LEFT JOIN tblimages AS T2
ON T2.id = T1.maxid
ORDER BY messages.msg_id DESC

在tblimages中找到每个用户的max(id),然后使用它将每个用户加入该用户的最新照片.