sql - JOIN psql 中的三个表(SQL 查询)

Question

我有一个这样的表:

UsersDevices: user_id, device_id
registration_posusercompany: company_id, user_id
registation_companyprofile: company_id, company_name

我知道UsersDevices中的device_id，我现在想知道设备所属的company_name。为此，伪代码如下所示:

--> Get user_id from UsersDevices where device_id = (I know this device_id)
--> Get company_id with that user_id from registration_posusercompany
--> Get company_name with that company_id

我正在编写子查询来执行此操作，但与 JOIN 相比，子查询确实非常慢。如何使用 JOIN 实现此目的。谢谢

Answer 1

select rc.company_name 
from UsersDevices as u 
   join registration_posusercompany as rp on rp.user_id = u.user_id 
   join registation_companyprofile as rc on rc.company_id = rp.company_id 
where u.device_id = yourvalue