MySQL的 - 加入并计算记录数据

Question

我尝试通过用户ID，但结果计数的数据记录是总行的记录，我有以下 enter image description here

数据我使用的查询这里：

SELECT user.id, COUNT(upload.user_id), upload.file_name FROM upload Right JOIN user ON upload.user_id = user.id;

Answer 1

如果您想通过user_id来算，那么你就不需要JOIN可言，它可以是一个简单的GROUP BY与COUNT，例如：

SELECT user_id, COUNT(*) 
FROM upload 
GROUP BY user_id; 

Answer 2

我会做这样SELECT us.id, (select count(*) from upload where user_id=us.id), u.file_name FROM upload u, user us where u.user_id = us.id;