Question

我正在开发论坛。表结构是：

forum_threads:
  id: int unsigned, primary key
  forum_id: int unsigned
  flags: int unsigned. (1 - closed, 2 - important, etc.)
  views: int unsigned

forum_thread_views_count: (is a MEMORY table, needed to reduce IO operations)
  thread_id: int unsigned, primary key
  views: int unsigned

forum_posts:
  id: int unsigned, primary key
  thread_id: int unsigned
  author_id: int unsigned
  flags: int unsigned
  creation_date: int unsigned (unix timestamp)

我需要选择：forum_thread.id，forum_thread.flags，forum_thread.views，forum_thread_views_count.views，COUNT(forum_posts)，MIN(forum_posts.id)，MAX(forum_posts.id)由forum_thread.forum_id订购的forum_posts.creation_date DESC。首先必须选择重要的主题（旗帜和2）。

现在我有查询：

SELECT t.id, t.flags, t.views, tv.views, COUNT(p.id), MIN(p.id), MAX(p.id)
FROM forum_threads t
LEFT JOIN forum_thread_views_count tv ON tv.thread_id = t.id
LEFT JOIN forum_posts p ON p.thread_id = t.id
WHERE t.forum_id = 1
GROUP BY t.id
ORDER BY t.flags & 2 DESC, p.creation_date DESC;

这是有效的，但我认为它可以做得更好。

Answer 1

有两种方法可以让它变得更好。首先，除非有正确使用外连接的原因，否则请使用内连接。接下来，从

更改您的论坛

GROUP BY t.id

到

GROUP BY t.id, t.flags, t.views, tv,views

虽然MySQL允许您使select和group by子句不匹配，但可能会导致您获得不正确的结果。

优化困难的mySQL查询

1 个答案: