Question

我正在尝试在表格中列出一些数据。数据来自数据库，我的数据库中有3个表。

我正在尝试在这样的SQL语句中加入这三个表：

SELECT * FROM cases
LEFT JOIN users ON cases.fk_supporter = users.user_id
LEFT JOIN users ON cases.fk_creator = users.user_id

fk_supporter是用户的外键，因此是fk_creator，但不是同一个用户。如何正确地做到这一点？

Answer 1

您需要连接中相同表的唯一别名

SELECT * FROM cases c
LEFT JOIN users u1 ON c.fk_supporter = u1.user_id
LEFT JOIN users u2 ON c.fk_creator = u2.user_id

Answer 2

您只需将 ALIAS 名称提供给表格

即可

试试这个：

SELECT * 
FROM cases c
LEFT JOIN users u1 ON c.fk_supporter = u1.user_id
LEFT JOIN users u2 ON c.fk_creator = u2.user_id;

Answer 3

您可以在ALIAS表中使用users：

SELECT * FROM cases
LEFT JOIN users supporter ON cases.fk_supporter = supporter.user_id
LEFT JOIN users creator ON cases.fk_creator = creator.user_id

Answer 4

可能你会有LEFT JOIN之外的其他东西，尝试使用Alias名称的INNER JOIN作为@Saharsh和@Abhik提到 - 如：

SELECT * FROM cases C
INNER JOIN users U1 ON C.fk_supporter = U1.user_id
INNER JOIN users U2 ON C.fk_creator = U2.user_id

Answer 5

好吧，我让它像这样工作：

SELECT 
supporter.usr AS supporter_usr, 
supporter.user_id as support_id,
creator.usr AS creator_usr, 
creator.user_id as creator_id,
cases.* FROM cases


LEFT JOIN users AS supporter 
ON supporter.user_id = cases.fk_supporter

LEFT JOIN users AS creator 
ON creator.user_id = cases.fk_creator

两次加入同一张桌子

5 个答案: