MySQL的加入第三個表

Question

計數行我有三個的MySQL表是這樣的：

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

現在我想有以下結果：

client.*, network.name, number_of_activities_for_each_client 

其實我有這樣的select語句：

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

如何擴展語句？我也想看到所有的客戶。

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