试图获取mysql中的最后一条消息

Question

这是我的查询：

SELECT u.ProfilePic AS FriendPic, u.UserName AS FriendName, m.*
FROM (SELECT PhotographerId
      FROM Messages
      WHERE UserId=? OR PhotographerId=?
      GROUP BY PhotographerId
     ) AS m JOIN
     User AS u
     ON u.UserId = m.PhotographerId;

我正在尝试从表中进行 SQL 查询， - 从所有用户对中获取最后的消息 user ？作为发件人或收件人，并将它们与用户表连接起来以获取名称。我已经设法创建了这样的东西，但仍然想问是否有更简单的

我想获取我们在收件箱中看到的每个用户的摄影师姓名、个人资料照片和最后一条消息..

表 用户：头像、用户名、user_id

消息：用户 ID、摄影师 ID、消息、时间戳

Answer 1

试试这个：

SELECT m.userid AS 'User id', u1.profile_pic AS 'User pic', u1.username AS 'User name`,
m.photographerid AS 'Photographer id', u2.profile_pic AS 'Photographer pic', 
u2.username AS 'Photographer name`,
m.message, m.timestamp
FROM message m JOIN user u1 ON m.userid = u1.user_id
JOIN user u2 ON m.photographerid = u2.user_id
ORDER BY m.timestamp DESC LIMIT 1;

更新：

您可以通过以下查询获取用户的最新消息：

SELECT m.userid, a.photographerid, m.message, a.timestamp
FROM message m
JOIN (SELECT photographerid, MAX(timestamp) as timestamp
FROM message where userid = ?
GROUP BY photographerid
) a
ON m.photographerid = a.photographerid and m.timestamp = a.timestamp
WHERE m.userid = ?

UNION

SELECT a.userid, m.photographerid, m.message, a.timestamp
FROM message m
JOIN (SELECT userid, MAX(timestamp) as timestamp
FROM message where photographerid = ?
GROUP BY userid
) a
ON m.userid = a.userid and m.timestamp = a.timestamp
WHERE m.photographerid = ?

收到消息后，您可以将此查询的输出与用户表连接起来，以获取其他列的值，例如：

SELECT m.userid AS 'User id', u1.profile_pic AS 'User pic', u1.username AS 'User name`,
m.photographerid AS 'Photographer id', u2.profile_pic AS 'Photographer pic', 
u2.username AS 'Photographer name`,
m.message, m.timestamp
FROM (
    SELECT m.userid, a.photographerid, m.message, a.timestamp
    FROM message m
    JOIN (SELECT photographerid, MAX(timestamp) as timestamp
    FROM message where userid = ?
    GROUP BY photographerid
    ) a
    ON m.photographerid = a.photographerid and m.timestamp = a.timestamp
    WHERE m.userid = ?

    UNION

    SELECT a.userid, m.photographerid, m.message, a.timestamp
    FROM message m
    JOIN (SELECT userid, MAX(timestamp) as timestamp
    FROM message where photographerid = ?
    GROUP BY userid
    ) a
    ON m.userid = a.userid and m.timestamp = a.timestamp
    WHERE m.photographerid = ?
) m JOIN user u1 ON m.userid = u1.user_id
JOIN user u2 ON m.photographerid = u2.user_id;