mysql - 左外连接无法正常工作

Question

我正在尝试返回上传次数最多的前三名用户。然后，我计算了 3 个顶级用户中每个用户的上传次数。现在它只返回一个用户并且计数计算所有上传，即使上传不属于该用户。

这是我的表设置：

上传：（id、userID、姓名、位置、类型）

用户：（id、fname、lname、用户名、头像、国家、密码）

SELECT u.id, u.userID, COUNT(us.id) as top_nums, us.username, us.avatar, us.country 
FROM upload u LEFT OUTER JOIN user us ON us.id=u.userID 
ORDER BY top_nums DESC LIMIT 3

在此先感谢您的帮助！！

Answer 1

我认为此查询可以解决您的问题：

SELECT us.id, us.username, us.avatar, us.country, COUNT(u.id) top_nums 
FROM `user` us 
LEFT JOIN upload u ON us.id = u.userId 
GROUP BY u.userID 
ORDER BY top_nums DESC LIMIT 3;

Answer 2

您的查询中缺少GROUP BY子句，

SELECT  u.id, u.userID, COUNT(us.id) as top_nums, us.username, us.avatar, us.country 
FROM    upload u 
        LEFT OUTER JOIN  user us 
            ON us.id=u.userID 
GROUP BY u.id, u.userID, us.username, us.avatar, us.country 
ORDER BY top_nums DESC 
LIMIT 3

但请记住，此查询不会处理关系。

Answer 3

我想你想这样做：

select      u.id, u.fname, u.lname, count(*)
from        user u
left outer join upload up on u.id = up.userid
group by    u.id, u.fname, u.lname
order by    count(*) desc

Answer 4

select us.username, us.avatar, us.country ,
(select count(*) from upload u where u.id=us.id) as no_of_uploads 
from users us order by 4 desc limit 3;