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

2023年5月19日 232次阅读

我正在开发一个聊天系统,会话列表必须显示两件事：

>发送消息的人的最后消息(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！

最佳答案 可能这有帮助

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

见IF mysql operator

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