MYSQL：如何从与另一列中的值相关的列返回值

Question

我正在努力表达这一点，更不用说在MYSQL中执行了。如何在（1,2,3,4,5,6,7,8）中返回userId.X和permissionId的userId X？

以下示例应返回6.

MariaDB [mailserver]> select * from user2permission;
+--------------+--------+
| permissionId | userId |
+--------------+--------+ 
|            1 |      5 |
|            1 |      6 |
|            2 |      6 |
|            2 |      7 |
|            3 |      6 |
|            4 |      6 |
|            5 |      6 |
|            6 |      6 |
|            7 |      6 |
|            8 |      6 |
+--------------+--------+

Answer 1

这种查询可以使用Group By子句编写，并根据where子句中应用的过滤计算实例

SELECT userId
FROM user2permission 
WHERE permissionId  IN (1,2,3,4,5,6,7,8)
GROUP BY userId 
HAVING COUNT(*) = 8

Answer 2

您希望仅显示具有所有必需权限条目的用户。想到两种解决方案：

select *
from users
where userid in (select userid from user2permission where permissionid = 1)
  and userid in (select userid from user2permission where permissionid = 2)
  ...

和

select userid,
from user2permission
group by userid
having count(case when permissionid = 1 then 1 end) > 0
   and count(case when permissionid = 2 then 1 end) > 0
   ...

当我说“春天”时，我的意思是确切地说=没有太多思考:-) Rizwan的聚合解决方案就是你应该使用的。