Question

我在mysql中有以下三个表格。

postid | post_content =＆gt;的帖子

commentid |发布| comment_content =＆gt;的评论

commentvoteid |评论|选民=＆gt;的 comment_votes

我想获取comments的所有counting its votes，post。

commentid | comment_content | comment_votes =＆gt;的 my_result

我尝试了以下查询但未获得所需的结果。

SELECT commentid,comment_content,count_comments.total AS comment_votes
FROM comments
INNER JOIN(SELECT COUNT(*) AS total FROM comment_votes WHERE comment=comments.commentid) AS count_comments
WHERE post={$postId}

是否可以按我的意愿获取结果？我怎么能这样做？

Answer 1

您可以使用GROUP BY来实现您的目标：

SELECT commentid,comment_content,COUNT(*) AS total
FROM comments
INNER JOIN comment_votes ON (comment_votes.comment=comments.commentid)
WHERE post={$postId}
GROUP BY commentid;

Answer 2

您正在尝试的方法使用相关子查询。您可以这样做，但相关子查询需要进入select子句：

SELECT c.commentid, c.comment_content,
       (SELECT COUNT(*) FROM comment_votes cv WHERE cv.comment = c.commentid
       ) AS comment_votes
FROM comments c
WHERE post={$postId};

通常情况下，我更喜欢group by方法，但有时在MySQL中这可能会更快。

Answer 3

也许是这样的：

select a.commentid, a.comment_content, count(b.*) as total from (
select commentid, comment_content from comments where post={$postId}) a
join comment_votes b on b.comment = a.commentid
group by a.commentid, a.comment_content;

得到所有评论，包括对一篇文章的投票

3 个答案: