mysql 在第三个表中加入计数行

Question

我有三个这样的 mySQL 表：

client                   network                   activities
\_id                     \_id                      \_id
\_name                   \_name                    \_client_id
\_[...]                  \[...]                    \_[...]
\_network_id

现在我想得到以下结果：

client.*, network.name, number_of_activities_for_each_client

其实我有这个选择语句：

select client.*, network.name 
from client 
left join network 
on client.network_id = network.id

如何扩展语句？我也想看看所有的客户。

Answer 1

SELECT c.*, n.name, COUNT(a.id) number_of_activities_for_each_client
FROM clients c
LEFT JOIN network n
ON n.id = c.network_id
LEFT JOIN activities a
ON a.client_id = c.id
GROUP BY c.id