Question

我已经使用PHP和mysql创建了一个小型消息传递系统。我已在消息表中将我的用户与sender和receiver相关联。我可以列出2个用户之间的对话。但是我无法通过每种对话显示1条消息结果的方法！

假设我有用户1,2和3.所以我的消息表可能如下所示：

===================================================================
    ID    ||    sender    ||    receiver    ||    text    ||    date
===================================================================
    1     ||       1      ||        2       ||    Hello!  ||    timestamp stuff
    2     ||       2      ||        1       ||      Hi!   ||
    3     ||       1      ||        3       ||    Boo!    ||

所以对话链接为

SELECT * FROM messages WHERE (sender=1 OR sender=2) AND (receiver=1 OR receiver=2);

这样我就能得到2个用户之间的完整对话（非常简化）。

回到问题但是，如何从每个对话中获得1条消息？

我尝试过这样的事情：

(SELECT m.text,m.date,sender.username,receiver.username 
FROM messages AS m 
INNER JOIN users AS sender on m.sender=user.ID 
INNER JOIN users AS receiver ON receiver.ID=m.receiver 
WHERE m.sender=1 OR m.receiver=1
ORDER BY messages.date DESC LIMIT 1);

但显然这并不是我想要的，因为只返回一行。我想我知道我需要做什么，我只是不知道该怎么做？我想我需要这样的东西：

SELECT sender.username,receiver.username,m.text,m.date FROM messages AS m 
INNER JOIN users AS sender ON sender.ID=m.sender
INNER JOIN users AS receiver ON receiver.ID=m.receiver
LEFT JOIN (SELECT mes.ID 
              FROM messages AS mes
              WHERE mes.sender=1 OR mes.receiver=1 
              ORDER BY mes.date DESC LIMIT 1) AS convo
ON convo.ID=m.ID;

这样的事情会起作用吗？

如果你想看到我的完整sql：

(SELECT sender.ID AS senderID,sender.username AS senderUsername,sender.firstname AS senderFirstname,sender.lastname AS senderLastname,sender.othername AS senderOthername,sender.url_name AS senderUrl_name,senderI.path as sender_default_image,
                                                        receiver.ID AS receiverID,receiver.username AS receiverUsername,receiver.firstname AS receiverFirstname,receiver.lastname AS receiverLastname,receiver.othername AS reciverOthername,receiver.url_name AS recieverUrl_name,receiverI.path as reciever_default_image,
                                                        messages.message,messages.date,messages.read
                FROM '.$wpdb->prefix.'fishy_messages AS messages
                INNER JOIN '.$wpdb->prefix.'fishy_users AS sender ON sender.ID=messages.sender
                LEFT JOIN '.$wpdb->prefix.'fishy_profile_default_image AS senderDP ON senderDP.userID=sender.ID
                INNER JOIN '.$wpdb->prefix.'fishy_users AS receiver ON receiver.ID=messages.receiver
                LEFT JOIN '.$wpdb->prefix.'fishy_profile_default_image AS receiverDP ON receiverDP.userID=receiver.ID
                LEFT JOIN '.$wpdb->prefix.'fishy_images AS senderI ON senderI.ID=senderDP.imageID
                LEFT JOIN '.$wpdb->prefix.'fishy_images AS receiverI ON receiverI.ID=receiverDP.imageID
                    WHERE messages.sender=%d OR messages.receiver=%d ORDER BY messages.date DESC LIMIT 1)

是的我使用wordpress：p

Answer 1

要返回单个结果，在外部查询上给出Limit 1，您已在INNER查询中给出。

SELECT sender.username,receiver.username,m.text,m.date FROM messages AS m 
INNER JOIN users AS sender ON sender.ID=m.sender
INNER JOIN users AS receiver ON receiver.ID=m.receiver
LEFT JOIN (SELECT mes.ID 
              FROM messages AS mes
              WHERE mes.sender=1 OR mes.receiver=1 
              ORDER BY mes.date DESC LIMIT 1) AS convo
ON convo.ID=m.ID GROUP BY convo.ID ;

Answer 2

SELECT sender.ID AS senderID,sender.username AS senderUsername,sender.firstname AS senderFirstname,sender.lastname AS senderLastname,sender.url_name AS senderUrl_name,receiver.ID AS receiverID,receiver.username AS receiverUsername,receiver.firstname AS receiverFirstname,receiver.lastname AS recieverLastname,receiver.url_name AS recieverUrl_name,messages.message,messages.date,messages.read 
FROM wp_6_fishy_messages AS messages 
INNER JOIN wp_6_fishy_users AS sender ON sender.ID=messages.sender 
INNER JOIN wp_6_fishy_users AS receiver ON receiver.ID=messages.receiver 
WHERE messages.sender=1 OR messages.receiver=1
GROUP BY messages.sender,messages.receiver ORDER BY messages.date DESC

因为我在发送方和接收方之间没有conversation ID/key作为我的对话。我把这两个人分组了！这给了我这些用户之间的最后两条消息：）

消息系统，显示对话列表

2 个答案: