MySQL 连接两个潜在的字段名称

Question

对于我正在开发的一个网站，我的任务是实现一个私有(private)消息系统。 我的基本场景是，数据库中有多个消息条目，每个条目包含一个发送者和一个接收者。然而，“当前用户”应该能够看到这两条消息，因为它们都与他相关。 问题是，我只对其他用户的数据感兴趣，而不是我自己的数据。但“当前用户”既可以是发件人，也可以是收件人。

我在这里的查询完成了这项工作，但它并不优雅。我加入两个用户，然后使用 IF 决定我应该获取哪些数据。

SELECT
    IF(m.sender = ?, 1, 0) AS isself,
    IF(m.sender = ?, u_recipient.id, u_sender.id) AS other_id,
    IF(m.sender = ?, u_recipient.displayName, u_sender.displayName) AS other_name,
    IF(m.sender = ?, u_recipient_avatar.url, u_sender_avatar.url) AS other_avatar,
    m.text AS text
FROM messages AS m
    LEFT JOIN user AS u_sender
        ON u_sender.id = m.sender
    LEFT JOIN avatars AS u_sender_avatar
        ON u_sender_avatar.id = u_sender.avatarId

    LEFT JOIN user AS u_recipient
        ON u_recipient.id = m.recipient
    LEFT JOIN avatars AS u_recipient_avatar
        ON u_recipient_avatar.id = u_recipient.avatarId
WHERE ( m.sender = ? OR m.recipient = ? )
    AND UNIX_TIMESTAMP(m.timestamp) > ?
ORDER BY m.timestamp ASC
LIMIT 100

所以基本上，我的问题是，有没有更优雅的方法来做到这一点？将发送者/接收者 int 存储到 1 个单个表中以便在连接中重用？否则，这是否会消耗性能(连接我不需要的表？)。或者我应该在应用程序本身中将它们分开？

提前致谢!

Answer 1

看到我不允许编辑其他答案，该答案部分正确。 我的答案是基于 Ben 的答案，但删除了语法错误。

SELECT d.isself, other_id, u.displayName AS other_name, a.url AS other_avatar, text
FROM
(
    SELECT 0 AS isself, m.sender AS other_id, m.timestamp, m.text
    FROM messages AS m
    WHERE m.recipient = ?

    UNION

    SELECT 1 AS isself, m.recipient AS other_id, m.timestamp, m.text
    FROM messages AS m
    WHERE m.sender = ?
) AS d
    LEFT JOIN user AS u 
        ON u.id = d.other_id
    LEFT JOIN avatars AS a
        ON a.id = u.avatarId
WHERE UNIX_TIMESTAMP(timestamp) > ?
ORDER BY m.timestamp ASC
LIMIT 100