MySQL聊天系统显示发送者/接收者的最后一条消息和其他人的姓名答案

【问题标题】：MySQL chat system to display last message of sender/receiver AND name of other personMySQL聊天系统显示发送者/接收者的最后一条消息和其他人的姓名
【发布时间】：2014-04-10 21:09:14
【问题描述】：

我正在开发一个聊天系统，会话列表必须显示 2 件事：

发送消息的人（我又名当前用户或其他用户）的最后一条消息
其他用户的姓名

我遇到问题的部分是第二点。当前查询显示每个对话的最后一条消息，但在我（当前用户）发送最后一条消息的情况下，应该显示其他用户的名称而不是我的姓名。

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

在本例中，我是 Andufo (id_user = 1)。如果有帮助，这里是sqlfiddle link。谢谢！

【问题讨论】：

为了所有回答者的利益，您是否愿意出于性能/简单性的原因更改您的数据库结构，或者您只想根据您当前的结构获得答案？不是说它需要它，但其他人可能！
SQL Fiddle 链接似乎不起作用，您可以使用表结构、示例数据和所需结果编辑您的问题吗？
你想要来自用户的名字还是给用户的名字？
@halfer 是的，我愿意更改某些结构，唯一的规则是始终有一个单独的消息表和一个单独的用户表。
@AjayPatel 始终是“收件人”名称。它与 iMessage、Whatsapp、LINE 等收件箱非常相似。

标签： mysql sql database chat

【解决方案1】：

这可能有帮助

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

见IF mysql operator

【讨论】：

@andufo，你检查了吗？
抱歉，刚放假回来，我明天重新开始工作，但我会在几分钟后尝试查询。

【解决方案2】：

这个查询会有所帮助：

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,
         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

【讨论】：