Question

我想为列创建一个子选择，具有特定的计数。

通常这不是问题，但在这种情况下，我需要将当前列的ID作为过滤器。

例如，我有一个表Rooms：

RoomID  Name 
---------------
  1     Room 1
  2     Room 2
  3     Room 3

所有房间都有客户，例如

ClientID   RoomID   ClientName
-------------------------------
   1         1      Client1
   2         1      Client2
   3         2      Client3

还有一个ClientUsage表，例如

ID ClientID StateID
-------------------
1     1       1
2     2       1
3     3       0

现在我要显示所有房间，包括所有客户的数量（例如StateID = 1）

结果应为：

ID, RoomID, CountOfClients, CountOfClientsWithStateID = 1

前三件事很容易，使用这个：

SELECT 
    ID, Name,
    (SELECT COUNT(*) AS Count
     FROM Client
     WHERE (RoomID = T1.ID)) AS ClientCount
FROM  
    Room AS T1

但现在我需要Client.ID作为参考来获取状态 - 任何想法如何解决？

尝试使用类似的东西，但这不起作用：

SELECT 
    ID, Name,
    (SELECT COUNT(*) AS Count
     FROM Client AS T2
     WHERE (RoomID = T1.ID)) AS ClientCount,
    (SELECT COUNT(*) AS Count
     FROM ClientUsage
     WHERE (ClientUsage.ClientID = T2.ID) AND (StateID = 1)) AS ClientFreeCount
FROM 
    Room AS T1

提前致谢

Answer 1

您可以使用以下内容：

SELECT ID, Name,
       (SELECT COUNT(*) AS Count
          FROM Client AS T2
         WHERE (RoomID = T1.ID)) AS ClientCount,
       (SELECT COUNT(*) AS Count
          FROM ClientUsage
          JOIN Client ON ClientUsage.ClientID = Client.ID
         WHERE (StateID = 1)
           AND (Client.RoomID = T1.ID)
       ) AS ClientFreeCount
  FROM Room AS T1

Answer 2

  SELECT id AS ClientUsageID, 
                roomid AS RoomID, 
                count(cliendid) AS CountClientID,
                StateID AS CountOfClientsWithStateID 
  FROM room R join client C
    ON R.RoomID  =C.RoomID  
    join ClientUsage  CL
    on C.ClientID   =CL.ClientID  
    where StateID=1

在SQL Server中进行子选择

2 个答案: