选择三个表和统计

Question

我有三个表，我需要选择电子邮件和计数表A和表B之间的关系，例如：

表A：

ID | email 
1 | test@test 
2 | test2@test 
3 | test3@test 

表B：

UID | username 
11 | James 
22 | Gabriel 
33 | Jonas 

表C：（A和B之间的关系）

ID | email_id | username_id 
    1 | 1  | 11 
    2 | 1  | 22 
    3 | 2  | 33 

期待结果：

Email  | Totalrelation 
test@test | 2 
test2@test | 1 

我想：

select tableA.email, 
    COUNT(distinct tableC.email_id) AS total from tableA as tableA, tableC as tableC GROUP BY tableC.email_id 

但它没有工作，我总不会错。我该怎么做？

Answer 1

连接表，组的数据和统计数为每个组

select a.email, count(c.id) as cnt 
from tableA a 
left join tableC c on c.email_id = a.id 
group by a.email