mysql 在第三个 table 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

现在我想要得到以下结果：

client.*, network.name, number_of_activities_for_each_client

实际上我有这个select-声明：

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

如何扩展语句？我也想见见所有客户

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

mysql 在第三个 table 中加入计数行

mysql join count lines in third table

mysql

join

count

multiple-tables