Php 选择帖子、最后3条评论以及所有评论的计数

选择帖子、最后3条评论以及所有评论的计数 我的代码：

它给我所有的评论，但我只需要3个，我添加了SELECT count（postid）作为所有的评论，最后限制为0，3

SELECT count(postid) as all_comments, p.*, u.id, u.username username, u.usersurname usersurname, u.usermainphoto userphoto, GROUP_CONCAT(c.text SEPARATOR 'a!k@h#md%o^v&') commenttext,GROUP_CONCAT(c.likes SEPARATOR '-') commentlikes,GROUP_CONCAT(c.dislikes SEPARATOR '-') commentdislikes, GROUP_CONCAT(c.commentdate) commentdate, GROUP_CONCAT(u2.username) commentauthorname, GROUP_CONCAT(c.anonim) commentanonym, GROUP_CONCAT(c.id) commentid, GROUP_CONCAT(u2.id) commentauthorid, GROUP_CONCAT(u2.usersurname) commentauthorsurname, GROUP_CONCAT(u2.usermainphoto) commentauthorphoto, GROUP_CONCAT(c.commentphotoid) commentphotoid
FROM posts p
LEFT JOIN comments c ON c.post = p.postid AND c.commentdel=0
LEFT JOIN users u ON u.id = p.postauthorid
LEFT JOIN users u2 ON u2.id = c.author
WHERE p.postwallid = :id AND p.postdel=0
GROUP BY postid
ORDER BY postid DESC
LIMIT 0, 3

---

你需要一个时间戳或计数器来确定哪三条评论是你想要的。在下面的尖括号之间添加该列名

SELECT p.*, u.id, u.username username, u.usersurname usersurname, u.usermainphoto userphoto, GROUP_CONCAT(c.text SEPARATOR 'a!k@h#md%o^v&') commenttext,GROUP_CONCAT(c.likes SEPARATOR '-') commentlikes,GROUP_CONCAT(c.dislikes SEPARATOR '-') commentdislikes, GROUP_CONCAT(c.commentdate) commentdate, GROUP_CONCAT(u2.username) commentauthorname, GROUP_CONCAT(c.anonim) commentanonym, GROUP_CONCAT(c.id) commentid, GROUP_CONCAT(u2.id) commentauthorid, GROUP_CONCAT(u2.usersurname) commentauthorsurname, GROUP_CONCAT(u2.usermainphoto) commentauthorphoto, GROUP_CONCAT(c.commentphotoid) commentphotoid
FROM posts p
LEFT JOIN comments c ON c.post = p.postid AND c.commentdel = 0
LEFT JOIN users u ON u.id = p.postauthorid
LEFT JOIN users u2 ON u2.id = c.author
WHERE p.postwallid = :id AND p.postdel = 0
    and (
        select count(*) from comments as c2
        where c2.postid = p.postid and c2.commentdel = 0
        and c2.<timestamp> <= c.timestamp
    ) < 3
GROUP BY postid
ORDER BY postid DESC

---

首先，对于GROUP BY，您应该只选择GROUP BY节中的原始字段，或者选择的字段应该通过聚合函数（min、max、sum等）进行。然后，我在你的查询中看不到COUNT函数，因此你将无法计算评论。在这种情况下，你限制了帖子，但我需要限制评论。

SELECT p.*, u.id, u.username username, u.usersurname usersurname, u.usermainphoto userphoto, GROUP_CONCAT(c.text SEPARATOR 'a!k@h#md%o^v&') commenttext,GROUP_CONCAT(c.likes SEPARATOR '-') commentlikes,GROUP_CONCAT(c.dislikes SEPARATOR '-') commentdislikes, GROUP_CONCAT(c.commentdate) commentdate, GROUP_CONCAT(u2.username) commentauthorname, GROUP_CONCAT(c.anonim) commentanonym, GROUP_CONCAT(c.id) commentid, GROUP_CONCAT(u2.id) commentauthorid, GROUP_CONCAT(u2.usersurname) commentauthorsurname, GROUP_CONCAT(u2.usermainphoto) commentauthorphoto, GROUP_CONCAT(c.commentphotoid) commentphotoid
FROM posts p
LEFT JOIN comments c ON c.post = p.postid AND c.commentdel = 0
LEFT JOIN users u ON u.id = p.postauthorid
LEFT JOIN users u2 ON u2.id = c.author
WHERE p.postwallid = :id AND p.postdel = 0
    and (
        select count(*) from comments as c2
        where c2.postid = p.postid and c2.commentdel = 0
        and c2.<timestamp> <= c.timestamp
    ) < 3
GROUP BY postid
ORDER BY postid DESC

(
select count(*) from comments as c2
where c2.postid = c.postid and c2.commentdel = 0
) as comment_count