Question

考虑两个表：USERS和TASKS用于任务交付应用

USERS
userID | email | name

TASKS
userID | designator_userUNIQUE | destination_userUNIQUE

要从destination_user表中获取users全名，我使用以下查询可以正常运行：

     SELECT * 
       FROM tasks 
 INNER JOIN users ON users.userID = tasks.destination_userUNIQUE
      WHERE tasks.client='$clientUNIQUE' 
   ORDER BY tasks.date DESC, tasks.time DESC

但是，如果我想使用以下查询从designator_userUNIQUE获取全名，则只会生成sql错误（mysql_numrows() expects parameter 1 to be resource）。

     SELECT * 
       FROM tasks
 INNER JOIN users ON users.userID = tasks.destination_userUNIQUE
 INNER JOIN users ON users.name = tasks.designator_user UNIQUE
      WHERE tasks.client='$clientUNIQUE' 
   ORDER BY tasks.date DESC, tasks.time DESC

有什么想法吗？

Answer 1

您需要为您加入的users表的每个实例提供不同的别名，以防止出现歧义。

SELECT *
FROM tasks AS t
INNER JOIN users AS dest ON dest.userID = t.destination_userUNIQUE
INNER JOIN users AS desig ON desig.userID = t.designator_userUNIQUE
WHERE t.client='$clientUNIQUE' 
ORDER BY t.date DESC, t.time DESC

Double JOIN获得两个不同的参数？

1 个答案: