Question

我有一个帖子的数据库表。我有另一个包含注释的db表，其中包含comment_id（ai）列和post_id附加到的列。

我想查询所有帖子一次的查询列表，按上次发布的评论排序。

问题是我无法找出sql查询来做到这一点。无论我尝试什么，我都会列出所有评论。我对mysql非常熟练或经验丰富，但我尝试使用不同的＆＃34;加入＆＃34;。有没有办法做到这一点？

Answer 1

SELECT posts.*, comments.last_one
FROM posts
LEFT JOIN 
 (SELECT MAX(updated) as last_one, post_id
  FROM comments
  GROUP BY post_id
 ) as comments
ON comments.post_id = posts.id
ORDER BY comments.last_one DESC

Answer 2

SELECT distinct p.* FROM posts as p, comments as c 
WHERE p.post_id = c.post_id ORDER BY c.time DESC

我刚刚假设你的关系模式。您可能需要调整查询。

替代方法：使用last_comment_time作为字段创建视图。

CREATE VIEW posts AS 
(SELECT *, (SELECT time FROM comments WHERE post_id = p.post_id ORDER BY time DESC LIMIT 1) as last_comment_time
 FROM posts as p);

帖子，评论和高级SQL过滤

2 个答案: