誰從外鍵返回一個值其空和非空

Question

我有兩個數據庫，我使用它們之間的關係。 但是有些行沒有它們之間的關係。

例如：

Select user.name as name, account.code as code 
from user u 
JOIN account acc ON u.account_id = acc.id 

我想在代碼檢索NULL和NOT NULL值

Answer 1

那麼你應該像

Select user.name as name, account.code as code 
from user u 
LEFT JOIN account acc ON u.account_id = acc.id