mysql - 从同一个表中选择两个不同的值(mysql)

Question

我正在做一个小论坛。我想要的是在列出论坛主题时，显示主题创建者和最后回复者的用户名和头像。

当前查询(目前只查找主题创建者的头像+用户名)为:

SELECT 
    forum_topics.primkey,
    forum_topics.title,
    forum_topics.creatorid, 
    forum_topics.last_reply_poster, 
    users.username,
    users.avatar,
    forum_tracks.lastmark 
FROM 
    users,
    forum_topics 
    LEFT JOIN forum_tracks 
        ON forum_tracks.userid='".$_SESSION['loggeduserkey']."' 
        AND forum_tracks.topic_id=forum_topics.primkey 
WHERE 
    forum_topics.cat_id='".$forum_id."' 
    AND users.userkey=forum_topics.creatorid 
ORDER BY ...;

那么，我如何修改上面的查询，以便同时找到 last_reply_poster(用户 ID)的用户名+头像？

谢谢!

Answer 1

你必须分两次加入用户表:

SELECT 
    forum_topics.primkey,
    forum_topics.title,
    forum_topics.creatorid, 
    forum_topics.last_reply_poster, 
    users.username,
    users.avatar,
    u2.username,
    u2.avatar,
    forum_tracks.lastmark 
FROM 
    users,
    users as u2,
    forum_topics 
    LEFT JOIN forum_tracks 
        ON forum_tracks.userid='".$_SESSION['loggeduserkey']."' 
        AND forum_tracks.topic_id=forum_topics.primkey 
WHERE 
    forum_topics.cat_id='".$forum_id."' 
    AND users.userkey=forum_topics.creatorid
    AND u2.userkey=forum_topics.last_reply_poster
ORDER BY ...;