Question

我正在开发一个聊天系统，会话列表必须显示两件事：

发送邮件的人的最后一条消息（我是当前用户或其他用户）
其他用户的名称

我遇到问题的部分是第二点。当前查询显示每个会话的最后一条消息，但在我（当前用户）发送最后一条消息的情况下，而不是我的名字，它应该显示另一个用户的名字。

SELECT SQL_CALC_FOUND_ROWS
    u.id_user AS id,
    i.id_user_from,
    i.id_user_to,
    u.name AS name,
    UNIX_TIMESTAMP(i.date_msg) AS date_msg,
    i.message AS msg

    FROM inbox AS i
    INNER JOIN user AS u ON (u.id_user = i.id_user_from OR u.id_user = i.id_user_to)

    WHERE id_msg IN
    (SELECT MAX(id_msg) AS id FROM
    (
        SELECT id_msg, id_user_from AS id_with
        FROM inbox
        WHERE id_user_to = 1

        UNION ALL

        SELECT id_msg, id_user_to AS id_with
        FROM inbox
        WHERE id_user_from = 1) AS t

        GROUP BY id_with
    )

    ORDER BY i.id_msg DESC

在这个例子中，我是 Andufo （id_user = 1）。如果它有帮助，这是一个sqlfiddle link。谢谢！

Answer 1

可能有帮助

SELECT SQL_CALC_FOUND_ROWS
    u.id_user AS id,
    i.id_user_from,
    i.id_user_to,
    u.name AS name,
    UNIX_TIMESTAMP(i.date_msg) AS date_msg,
    i.message AS msg

    FROM inbox AS i
    INNER JOIN user AS u ON u.id_user = IF(i.id_user_from = 1 /*me*/, i.id_user_to, i.id_user_from)

    WHERE id_msg IN
    (SELECT MAX(id_msg) AS id FROM
    (
        SELECT id_msg, id_user_from AS id_with
        FROM inbox
        WHERE id_user_to = 1

        UNION ALL

        SELECT id_msg, id_user_to AS id_with
        FROM inbox
        WHERE id_user_from = 1) AS t

        GROUP BY id_with
    )
    ORDER BY i.id_msg DESC

请参阅IF mysql operator

Answer 2

此查询有助于：

SELECT SQL_CALC_FOUND_ROWS
       u.id_user AS id,
       i.id_user_from,
       i.id_user_to,
       u.name AS name,
       UNIX_TIMESTAMP(i.date_msg) AS date_msg,
       i.message AS msg
    FROM inbox AS i,
         user  AS u,
         (SELECT MAX(id_msg) AS id_max,
                 id_with
              FROM (
                    SELECT id_msg,
                           id_user_from AS id_with
                        FROM inbox
                        WHERE id_user_to = 1
                    UNION ALL
                    SELECT id_msg,
                           id_user_to
                        FROM inbox
                        WHERE id_user_from = 1
                   ) AS t
              GROUP BY id_with) AS m
    WHERE i.id_msg  = m.id_max
      AND u.id_user = m.id_with
    ORDER BY i.id_msg DESC

MySQL聊天系统显示发件人/收件人的最后一条消息和其他人的姓名

2 个答案: