mysql - 如何向此查询添加附加条件（使用 CASE）？

Question

到目前为止，这是我的查询：

SELECT
posts.title
, SUM(CASE comments.status WHEN 'approved' THEN 1 END) AS commentsCount
FROM posts
INNER JOIN comments
ON comments.postID = posts.id
WHERE
posts.status = ?
GROUP BY
posts.title
ORDER BY
commentsCount DESC
LIMIT 5

我需要让它在它得到时也检查comment.flagged= 0 commentsCount。我尝试CASE在SUM()调用中添加额外的 s，但这导致了致命错误。我怎样才能做到这一点？

谢谢！

Answer 1

SELECT
posts.title
, SUM(IF ((comments.status='approved' AND  comments.flagged = 0),1,0)) AS commentsCount
FROM posts
INNER JOIN comments
ON comments.postID = posts.id
WHERE
posts.status = ?
GROUP BY
posts.title
ORDER BY
commentsCount DESC
LIMIT 5

Answer 2

似乎您真正想做的是：

SELECT
posts.title
, COUNT(*) AS commentsCount
FROM posts
INNER JOIN comments
ON comments.postID = posts.id
AND comments.status = 'approved'
AND comments.flagged = 0
WHERE
posts.status = ?
GROUP BY
posts.title
ORDER BY
commentsCount DESC
LIMIT 5

由于您只对commentswho statusis感兴趣'approved'，因此条件应该是 join 条件。

编辑：我已经更新了查询，假设您想要计算status等于'approved'和flagged等于的评论0。

Answer 3

基于 Josh Davis 的 SQL，这对我有用：

SELECT
posts.title
, posts.slug
, COUNT(comments.id) AS commentsCount
FROM posts
INNER JOIN comments
ON comments.postID = posts.id
AND comments.status = 'approved'
AND comments.flagged = 0
WHERE
posts.status = ?
GROUP BY
posts.title
ORDER BY
commentsCount DESC
LIMIT 5