mysql - 将子查询(不在)重写为Join

Question

大家好，是否可以重写查询:

select userid from User where userid not in(select userid from UserRole where roleid in(8));

作为加入？

问题是一个用户可能有多个角色
先感谢您。

mysql> desc User;  
+--------------------+-------------------+------+-----+---------+----------------+  
| Field              | Type              | Null | Key | Default | Extra          |  
+--------------------+-------------------+------+-----+---------+----------------+  
| userId             | int(11)           | NO   | PRI | NULL    | auto_increment |  
| userName           | varchar(50)       | YES  |     | NULL    |                |  

...以及其他用户相关列

mysql> desc UserRole;  
+--------+---------+------+-----+---------+-------+  
| Field  | Type    | Null | Key | Default | Extra |  
+--------+---------+------+-----+---------+-------+  
| userId | int(11) | NO   | PRI | 0       |       |  
| roleId | int(11) | NO   | PRI | 0       |       |  
+--------+---------+------+-----+---------+-------+  

Answer 1

我还没有测试过这个，但我认为它有效。

select userID from user 
left join UserRole 
on user.userID = UserRole.userID 
and UserRole.roleID = 8
where UserRole.roleID IS NULL