我有两个表如下。
user_id | username | first_name | role_type
-----------------------------------------------------------
1 | testuser1 | testu1 | student
2 | testuser2 | testu2 | student
3 | testuser3 | testu3 | student
4 | testuser4 | testu4 | student
5 | testuser5 | testu5 | student
6 | testuser6 | testu6 | admin
7 | testuser7 | testu7 | admin
-----------------------------------------------------------
user_id | username | approved_id
----------------------------------------------------------------------
1 | testuser1 | 3B888F52-50BC-11E2-B08B-99E5B2CADDF7
2 | testuser2 | 3B888F52-50BC-11E2-B08B-99E5B2CADDF7
3 | testuser3 | 3B888F52-50BC-11E2-B08B-99E5B2CADDF7
----------------------------------------------------------------------
我试过查询
SELECT users.* FROM users
WHERE users.username NOT IN(
SELECT users_approval.username FROM users_approval
WHERE users_approval.approved_id = "3B888F52-50BC-11E2-B08B-99E5B2CADDF7"
) AND users.role_type = "student"
并得到下面的结果
user_id | username | first_name | role_type
-------------------------------------------------------------
4 | testuser4 | testu4 | student
5 | testuser5 | testu5 | student
-------------------------------------------------------------
有没有办法使用 JOIN 来获取与上面相同的结果集?
非常感谢帮助。