SQL查询以显示表中只有一个值的行

我在SQL Server中编写SQL时遇到问题。在这里，我有三个表，分别名为

User

，

Client

，和

UserClient

。下面是表格内容的示例

客户端

idClient     | client
____________________________
1            | Client A
2            | Client B
3            | Client C

idUserClient | idUser     | idClient
____________________________________
1            | 1          | 1
2            | 1          | 2
3            | 2          | 1
4            | 2          | 3
5            | 3          | 1

用户

idUser       | User
____________________________
1            | User A
2            | User B
3            | User C

USERCLIENT

idClient     | client
____________________________
1            | Client A
2            | Client B
3            | Client C

idUserClient | idUser     | idClient
____________________________________
1            | 1          | 1
2            | 1          | 2
3            | 2          | 1
4            | 2          | 3
5            | 3          | 1

我需要一个查询来向用户显示

idClient=1

，并且从

USERCLIENT

表中只能有一个客户端。如上面的示例所示，查询的结果应该是

idUserClient | idUser     | idClient
_________________________________________
5            | 3          | 1

假设

（idUser，idClient）

是唯一索引：

SELECT USERCLIENT.idUser
FROM USER
   INNER JOIN USERCLIENT
       ON USER.idUser = USERCLIENT.idUser
WHERE USERCLIENT.idClient = 1
GROUP BY USERCLIENT.idUser
HAVING COUNT(*) = 1

宾果

---

根据你提到的数据，你可以通过两种方式得到你想要的结果

select * from userclient where idUser = 3

或

我不确定你到底想要什么，但这两个案例产生了结果

你有什么疑问？

这对我来说很有用

with cte AS
(
    SELECT 1 AS idUserClient, 1 AS idUser, 1 AS idClient 
    UNION
    SELECT 2 AS idUserClient, 1 AS idUser, 2 AS idClient 
    UNION
    SELECT 3 AS idUserClient, 2 AS idUser, 1 AS idClient 
    UNION
    SELECT 4 AS idUserClient, 2 AS idUser, 3 AS idClient 
    UNION
    SELECT 5 AS idUserClient, 3 AS idUser, 1 AS idClient 
)
SELECT * FROM cte c1
WHERE 
    idUserClient IN 
    (
        SELECT MIN(c2.idUserClient) FROM cte c2 GROUP BY c2.idUser HAVING COUNT(c2.idUser) = 1
    )

---

这将显示与客户端关联的用户

idClient=1

，并且仅显示该客户端：

SELECT
  MAX(idUserClient) AS idUserClient,
  idUser,
  MAX(idClient) AS idClient
FROM USERCLIENT
GROUP BY idUser
HAVING COUNT(*) = 1
   AND COUNT(CASE idClient WHEN 1 THEN 1 END) = 1

HAVING

子句检查用户的一组行是否正好包含一行，并且在“它们”中正好有一行

idClient=1

或者，SQL Server 2008允许您执行以下操作：

WITH ranked AS (
  SELECT
    *,
    rnk = ROW_NUMBER() OVER (
      PARTITION BY idUser
      ORDER BY CASE idClient WHEN 1 THEN 1 ELSE 0 END, idClient
    )
  FROM USERCLIENT
)
SELECT
  idUserClient,
  idUser,
  idClient
FROM ranked
WHERE rnk = 1
  AND idClient = 1

---

CTE对

USERCLIENT

中的行进行排序，这样，如果一个用户与

idClient=1

关联，而没有其他客户端，则相应的行被排序为1，否则

idClient=1

的行（如果存在这样的行）将获得不同的排序。因此，当从CTE中选择时，您只需在

rnk=1和idClient=1上进行筛选，用户不是一个好的字段名，它是一个保留关键字是的，这只是一个示例，我不使用它作为实际的表名。thx btw的信息。我需要得到一个用户，只有一个从表userclient客户端客户端。我怎么做？那也许天蝎座的回答会有帮助？呜呜呜！这个答案花了我100多分！！谢谢你的支持，酒水是开着的。。那边那个人：D