Question

SELECT p.*,
    u.user_id,
    u.user_name,
    count(c.comment_post_id) AS comments
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)
WHERE c.comment_added > NOW() - INTERVAL 1 HOUR
GROUP BY p.post_id    
ORDER BY count(c.comment_post_id) DESC

这会在过去一小时内按大部分评论排序的帖子列表。现在的问题是，上个小时有0个评论的帖子没有列表。

那么有没有办法让自评论创建以来每小时的平均评论排序？通过这种方式，所有帖子都会成为列表，并且讨论最多的帖子将始终排在最前面。

http://sqlfiddle.com/#!9/820044/1/0

编辑：

SELECT p.*, u.user_id, u.user_name, COUNT(c.comment_post_id) / (TIMESTAMPDIFF(HOUR, p.post_timestamp, SYSDATE()) + 1) AS rate 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(HOUR, p.post_timestamp, SYSDATE()) + 1) DESC

这就解决了这个问题。

Answer 1

在没有数据的情况下很难看到，但为了解决您的直接问题（即显示零最近评论帖子），您是否只想将约束移动到LEFT JOIN？

LEFT JOIN comments AS c
    ON (p.post_id = c.comment_post_id AND c.comment_added > NOW - INTERVAL 1 HOUR)

Answer 2

由于WHERE子句，您只选择在一小时内发表评论的帖子。您可以尝试的是：

SELECT p.*,
    u.user_id,
    u.user_name,
    SUM(c.comment_added > NOW() - INTERVAL 1 HOUR) AS comments
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(HOUR, p.post_timestamp, SYSDATE()) + 1) DESC

对于小时内的每个评论，布尔表达式c.comment_added > NOW() - INTERVAL 1 HOUR将为SUM(...)贡献一个。

对于第二部分，我们可以找到使用TIMESTAMPDIFF(HOUR, p.post_timestamp, SYSDATE())发布帖子所经过的小时数。因此，将评论数量与小时数相除，为我们提供了排序标准。但是我们在几个小时内添加一个以避免被零除。

发布每小时平均评论

2 个答案: