如何加入这些查询？

Question

我有两个问题：

SELECT * FROM `kamcms_forum_post` 
WHERE date=(SELECT max(date) 
FROM `kamcms_forum_post` 
WHERE `forum_topic_id` = [THERE IS PLACE FOR `forum_topic_id` from second query])

SELECT *, count(*) as posts 
FROM `kamcms_forum_topic` as t 
LEFT OUTER JOIN `kamcms_forum_post` as p  ON t.forum_topic_id = p.forum_topic_id 
GROUP BY t.forum_topic_id ORDER BY p.forum_post_id

第一个查询从主题获取最后一个帖子，第二个查询从主题和topic_name（从其他表）获取第一个帖子，并从主题获取所有帖子的计数。我如何加入这些查询？

输入：

kamcms_forum_topic kamcms_forum_post

输出：

标题来自forum_topic， 首先在forum_post上发布user_id和last date以及user_id。

Answer 1

第一个问题，您的第二个查询将始终至少返回1，以便对您的左连接主题进行计数。这应该与我对你的要求的理解非常接近。

SELECT t.title, p.user_id, p2.user_id, p2.date, count(p.forum_topic_id) as posts 
FROM kamcms_forum_topic as t 
LEFT OUTER JOIN kamcms_forum_post as p ON t.forum_topic_id = p.forum_topic_id 
LEFT OUTER JOIN kamcms_forum_post as p2 ON t.forum_topic_id = p2.forum_topic_id 
WHERE p.date=((SELECT MIN(date)
    FROM kamcms_forum_post sp where sp.forum_post_id = p.forum_post_id)
AND p2.date=((SELECT MAX(date)
    FROM kamcms_forum_post sp where sp.forum_post_id = p2.forum_post_id)
GROUP BY t.forum_topic_id ORDER BY p.forum_post_id

Answer 2

最终查询：

    SELECT t.title, p.user_id, p2.user_id, p2.date, count(p3.forum_post_id) as posts 
FROM kamcms_forum_topic as t 
LEFT OUTER JOIN kamcms_forum_post as p ON t.forum_topic_id = p.forum_topic_id 
LEFT OUTER JOIN kamcms_forum_post as p2 ON t.forum_topic_id = p2.forum_topic_id 
LEFT OUTER JOIN kamcms_forum_post as p3 ON t.forum_topic_id = p3.forum_topic_id 
WHERE p.date=(SELECT MIN(date)
    FROM kamcms_forum_post sp where sp.forum_topic_id = p.forum_topic_id)
AND p2.date=(SELECT MAX(date)
    FROM kamcms_forum_post sp where sp.forum_topic_id = p2.forum_topic_id)
GROUP BY t.forum_topic_id ORDER BY p.forum_post_id

感谢您的帮助