我在左连接中得到的查询总和计数错误。
这是两个单独的查询,它们分别给出正确的结果。
SELECT wallpaper_id FROM `contest_participants` WHERE contest_id=2
SELECT wallpaper_id, SUM(upvotes) FROM `contest_wallpaper_upvote` WHERE contest_id=2 GROUP BY wallpaper_id
我使用 join 来总结赞成票,如下
Select distinct p.wallpaper_id, sum(u.upvotes) from contest_participants p
Left join contest_wallpaper_upvote as u
On p.wallpaper_id = u.wallpaper_id
Where p.contest_id = 2 group by p.wallpaper_id
问题是,如果upvote 表中没有wallpaper_id 条目,则会给出错误的总和计数。
有人可以帮我解决这个查询吗?
谢谢
最佳答案
您可以像下面这样检查。如果u.wallpaper_id
为空,那么您可以添加0
,否则u.upvotes
Select distinct p.wallpaper_id, sum(if(u.wallpaper_id is null, 0, u.upvotes)) as upvotes from contest_participants p
Left join contest_wallpaper_upvote as u
On p.wallpaper_id = u.wallpaper_id AND u.contest_id = 2
Where p.contest_id = 2 group by p.wallpaper_id
关于php - 左连接中的总和计数错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/55432117/