Mysql 两次加入同一个表

我正试图在表格中列出一些数据。数据来自一个数据库，我的数据库中有3个表

我试图将这三个表连接到SQL语句中，如下所示：

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

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

---

fk_支持者

是用户的外键，

fk_创建者

也是用户的外键，但不是同一用户。如何正确执行此操作？

对于联接中的相同表，您需要唯一的别名

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

---

联接中的相同表需要唯一别名

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

---

您只需为表指定别名即可

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;

---

您只需为表指定别名即可

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;

---

您可以为

用户

表使用

别名

：

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

---

您可以为

用户

表使用

别名

：

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

---

可能你会有一些非左连接，尝试别名为@Saharsh和@Abhik的内部连接-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

---

可能你会有一些非左连接，尝试别名为@Saharsh和@Abhik的内部连接-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

---

好吧，我是这样工作的：

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

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

---

好吧，我是这样工作的：

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

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