Question

我有两张桌子。

“threads”包含列ID，forumID，标题，内容，unixtime

“comments”包含列ID，threadID，内容，unixtime

我想做一个mysql查询，它根据unixtime对这两个表中的所有行进行排序，但也没有两次显示相同的“threadID”。

以下查询将合并这两个表并对它们进行排序，但我无法删除线程的重复项。我尝试了一些GROUP BY和DISTINCT，但没有运气。

(SELECT unixtime, ID, threadID FROM comments)
UNION
(SELECT unixtime, ID, forumID FROM threads)
ORDER BY unixtime DESC

它用于显示论坛的首页，因此让同一个帖子出现不止一次是没有意义的。

编辑：我想展示最新评论和最新帖子。

Answer 1

SELECT unixtime, ID, type, type_id
FROM (( SELECT unixtime, ID, 'comment' AS type, threadID, forumID
        FROM (  SELECT unixtime, ID, threadID
                FROM comments
                ORDER BY unixtime DESC) AS h
        GROUP BY threadID)
        UNION ALL
      ( SELECT unixtime, ID, 'thread', ID, forumID
        FROM threads)
        ORDER BY unixtime DESC) AS h2
GROUP BY threadID
ORDER BY unixtime DESC

我改变了一些东西。我假设您想知道它的论坛或主题ID是不是？

Answer 2

如果您没有加入钥匙，可以轻松解决问题：

   Select DISTINCT tbl.unixtime from
    (
    (SELECT unixtime, ID, threadID FROM comments)
    UNION
    (SELECT unixtime, ID, forumID FROM threads)
    ORDER BY unixtime DESC))
    As tbl

Answer 3

这将帮助您获得唯一的threadID

(SELECT forumID, ID, unixtime FROM threads)
UNION
(SELECT distinct(threadID), ID, max(unixtime) FROM comments GROUPBY threadID)
ORDER BY unixtime DESC

合并和排序两个表

3 个答案: