如何检查每个组中是否存在值(分组后)

Question

假设我有一个订阅表:

uid  | subscription_type 
------------------------  
Alex | type1
Alex | type2
Alex | type3
Alex | type4
Ben  | type2
Ben  | type3
Ben  | type4

并且只想选择具有2个以上订阅但从未订阅类型1的用户

预期的结果是仅选择"Ben".

我很容易找到超过2个订阅的用户使用:

SELECT uid
FROM subscribes
GROUP BY uid
HAVING COUNT(*) > 2

但是如何检查组中是否存在某些值？

谢谢您的帮助!

Answer 1

试试这个查询:

SELECT uid 
FROM subscribes 
GROUP BY uid 
HAVING COUNT(*) > 2
   AND max( CASE "subscription_type"  WHEN 'type1' THEN 1 ELSE 0 END ) = 0

Answer 2

创建示例表：

CREATE TABLE subscribes
(
uid NVARCHAR(MAX),
subscription_type NVARCHAR(MAX)
)

插入值：

INSERT INTO subscribes
VALUES ('Alex', 'type1'), ('Alex', 'type2'), ('Alex', 'type3'), ('Alex', 'type4'),  ('Ben', 'type2'), ('Ben', 'type3'), ('Ben', 'type4')

SQL查询：

SELECT uid
FROM subscribes
GROUP BY uid
HAVING COUNT(*) > 2
AND MAX(CASE subscription_type WHEN 'type1' THEN 1 ELSE 0 END) = 0

输出：

======
|uid |
------
|Ben |
======

Answer 3

要检查某些东西是否不存在，请使用NOT EXISTS(...)：

SELECT uid
FROM subscribes su
WHERE NOT EXISTS (SELECT *
        FROM subscribes nx
        WHERE nx.uid = su.uid AND nx.subscription_type = 'type1'
        )
GROUP BY uid HAVING COUNT(*) > 2
        ;