Question

我有一个名为private_messages的SQL表，其中包含字段（id，from，to，message，stamp）。戳记字段对应于消息的日期

那么我需要什么查询：

1）在两个用户之间进行对话（按日期排序）？

我已经尝试了查询

(SELECT * FROM private_messages WHERE from=$my_id AND to=$other_id) 
UNION 
(SELECT * FROM private_messages WHERE from=$other_id AND to=$my_id) 
ORDER BY stamp
;

但不起作用......

2）获取我和其他用户之间的最后一条消息，每个消息都有一个不同的用户，按日期排序（例如构建一个像faceebook这样的收件箱）？

Answer 1

1）

SELECT  * 
FROM    private_messages a
WHERE   (a.from = $my_id AND a.to = $other_id) OR
        (a.from = $other_id AND a.to = $my_id)
ORDER   BY stamp DESC

2）。

SELECT  f.*
FROM
        (
            SELECT  *
            FROM    private_messages a
            WHERE  (LEAST(a.from, a.to), GREATEST(a.from, a.to), a.stamp) 
                    IN  (   
                            SELECT  LEAST(b.from, b.to) AS x, 
                                    GREATEST(b.from, b.to) AS y,
                                    MAX(b.stamp) AS msg_time
                            FROM    private_messages b
                            GROUP   BY x, y
                        )
        ) f
WHERE   $my_id IN (f.from, f.to)
ORDER   BY f.stamp DESC

Answer 2

你能试试吗？

SELECT x.* 
FROM (SELECT * FROM private_messages 
WHERE `to`='$my_id' OR `from`='$my_id' GROUP BY `to`, `from`) AS x 
ORDER BY x.stamp DESC ;

To，From可以是保留字。注意到x是表别名。

Answer 3

我过去做过这个，但是查询简单。可能这对你有用

      SELECT * FROM private_messages WHERE (from=$my_id AND to=$other_id) OR (from=$other_id AND to=$my_id) ORDER BY stamp

Answer 4

1）非常确定您需要围绕PHP变量引用，例如：

(SELECT * FROM private_messages WHERE from='$my_id' AND to='$other_id') UNION (SELECT * FROM private_messages WHERE from='$other_id' AND to='$my_id') ORDER BY stamp DESC

2）尝试类似：

SELECT * FROM (SELECT * FROM private_messages WHERE to='$my_id' OR from='$my_id' GROUP BY to, from) AS tmp_table ORDER BY stamp DESC

MySQL在两个用户之间进行对话

4 个答案: