mysql - sql 脚本中的奇怪错误

Question

SELECT p.*, u.user_id, u.user_name, 
       COUNT(c.comment_id) AS count, 
       COUNT(v.vote_post_id) / 
         (TIMESTAMPDIFF(MINUTE, v.vote_timestamp, SYSDATE()) + 1) AS rate
FROM posts AS p 
LEFT JOIN comments AS c ON (p.post_id = c.comment_post_id)
LEFT JOIN post_votes AS v ON (p.post_id = v.vote_post_id)
LEFT JOIN users AS u ON (p.postedby_id = u.user_id) 
GROUP BY p.post_id 
ORDER BY COUNT(v.vote_post_id) / 
     (TIMESTAMPDIFF(MINUTE, v.vote_timestamp, SYSDATE()) + 1) DESC

这是我正在编写的脚本。我没有很好地填充我的数据库来进行测试，但前两个结果会因评论而加倍。你能在这里看到任何明显的错误吗？我有另一个版本的脚本在这里运行良好:

SELECT p.*, u.user_id, u.user_name, 
       COUNT(c.comment_id) AS count
    FROM posts AS p 
    LEFT JOIN comments AS c ON (p.post_id = c.comment_post_id) 
    LEFT JOIN users AS u ON (p.postedby_id = u.user_id) 
    GROUP BY p.post_id 
    ORDER BY COUNT(c.comment_post_id) / 
       (TIMESTAMPDIFF(MINUTE, p.post_timestamp, SYSDATE()) + 1) DESC

Answer 1

多次投票会导致您的评论重复。如果您对 vote_post_id 进行GROUP BY，则希望对 post_votes 表进行子选择，以将每个帖子的总票数作为单个值获取.

由于 COUNT 是保留字，因此我不建议将其用作结果集中的列名称。

如果您只是获取评论计数而不是评论本身，那么您也会希望将其包含在子选择中，否则您将在帖子上加倍。

SELECT p.*, u.user_id, u.user_name, c.comment_count, 
    v.vote_count AS total_votes, 
    v.vote_count / (TIMESTAMPDIFF(MINUTE, p.post_timestamp, SYSDATE()) + 1) as votes_per_minute
FROM posts AS p 
LEFT JOIN (SELECT comment_post_id, COUNT(comment_post_id) AS comment_count FROM comments GROUP BY comment_post_id) AS c ON (p.post_id = c.comment_post_id)
LEFT JOIN (SELECT vote_post_id, COUNT(vote_post_id) AS vote_count FROM post_votes GROUP BY vote_post_id) AS v ON (p.post_id = v.vote_post_id)
LEFT JOIN users AS u ON (p.postedby_id = u.user_id) GROUP BY p.post_id 
ORDER BY v.vote_count / (TIMESTAMPDIFF(MINUTE, p.post_timestamp, SYSDATE()) + 1) DESC