有这样的表:
图片:
wall_id|picture_id|user_id|likes
1| 1| 1| 2
1| 2| 1| 0
2| 1| 1| 1
2| 2| 2| 2
对(wall_id,picture_id)是唯一的
喜欢者:
wall_id|picture_id|user_id
1| 1| 3
1| 1| 2
2| 1| 2
2| 2| 4
2| 2| 3
我想要得到这样的东西:
user_id|pictures_count|likes_count|likers_count
1| 3| 3| 2
2| 1| 2| 2
我尝试了这个:
select p.user_id as user_id,
count(p.user_id) as pictures_count,
sum(p.likes) as likes_count,
count(distinct l.user_id) as likers_count
from pictures p
left join likers l on p.wall_id = l.wall_id
and p.picture_id = l.picture_id
group by p.user_id
和
select pictures.user_id, count(pictures.user_id) as pictures_count,
sum(pictures.likes) as likes_count,
count(distinct likers.user_id) as likers_count
from pictures, likers
where pictures.picture_id = likers.picture_id
and pictures.user_id = likers.user_id
group by pictures.user_id
但是我得到这样的结果:
user_id|pictures_count|likes_count|likers_count
1| 4| 6| 2
2| 2| 4| 2
我应该怎么做才能得到正确的结果?
最佳答案
Join
是件奇怪的事情。当您有一个键并且两边都匹配多行时,您会得到更多的期望行。解决方案是预聚集每一侧的行。
数据模型有点复杂,因为您需要join
来查找likes
表的用户ID。
select p.user_id as user_id, p.pictures_count, p.likes_count, l.likers_count
from (select p.user_id, count(*) as pictures_count, sum(likes) as likes_count
from pictures p
group by p.user_id
) p left join
(select p.user_id, count(distinct l.user_id) as likers_count
from pictures p left join
likers l
on p.wall_id = l.wall_id and p.picture_id = l.picture_id
group by p.user_id
) l
on p.user_id = l.user_id;
注意,由于聚合是在子查询中完成的,因此外部查询中不再需要它。
关于sql - 来自多个表的sql count(),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/28740703/