如何添加子查询以返回相关行的计数答案

【问题标题】：How to add a subquery to return count of related rows如何添加子查询以返回相关行的计数
【发布时间】：2013-11-16 02:55:56
【问题描述】：

我有一个有效的 SELECT，它返回每个公司（即订户）的信息。某些描述性数据是从“代码”表上的内部连接返回的。我的问题是如何在结果中添加一个新列，该列是属于每个订阅者的用户数的计数。用户表中的 SubscriberID 是外键：

ALTER TABLE dbo.UserInfo WITH CHECK ADD CONSTRAINT FK_UserInfo_SubscriberID 
  FOREIGN KEY(SubscriberID) REFERENCES dbo.Subscriber (SubscriberID)
  ON UPDATE CASCADE
  ON DELETE CASCADE

我在下面添加了 LEFT OUTER JOIN 和 GROUP BY，但我无法弄清楚为什么解析器会抱怨 U.SubscriberID 是无效的列名）。

SELECT SubscriberID
  ,SubscriberName
  ,DaysUntilExpired
  ,SubscriptionStatus SubscriptionStatusCode
  , C.Description  SubscriptionStatus
  ,U.NumberUsers
FROM dbo.Subscriber S 
    JOIN dbo.CodeValue C ON S.SubscriptionStatus = C.Value
    JOIN dbo.CodeNamespace N ON N.ID = C.CodeNamespaceID AND N.Name = 'SubscriptionStatus'
    JOIN dbo.CodeValue V ON S.NotificationStatus = V.Value
    JOIN dbo.CodeNamespace X ON X.ID = V.CodeNamespaceID AND X.Name = 'NotificationStatus'
LEFT OUTER JOIN (SELECT Count(*) AS NumberUsers FROM dbo.UserInfo) AS U  
ON S.SubscriberID = U.SubscriberID 
GROUP BY 
    S.SubscriberID
  ,SubscriberName
  ,DaysUntilExpired
  ,S.SubscriptionStatus
  ,SubscriptionStatus

【问题讨论】：

(SELECT SubscriberID, Count(*) AS NumberUsers FROM dbo.UserInfo GROUP BY SubscriberID) AS U.

标签： sql sql-server tsql

【解决方案1】：

您可能正在寻找以下内容。您需要内联子查询

SELECT SubscriberID
  ,SubscriberName
  ,DaysUntilExpired
  ,SubscriptionStatus SubscriptionStatusCode
  , C.Description  SubscriptionStatus
  ,(SELECT Count(*) AS NumberUsers FROM dbo.UserInfo where SubscriberID = S.SubscriberID) AS NumberUsers
FROM dbo.Subscriber S 
    JOIN dbo.CodeValue C ON S.SubscriptionStatus = C.Value
    JOIN dbo.CodeNamespace N ON N.ID = C.CodeNamespaceID AND N.Name = 'SubscriptionStatus'
    JOIN dbo.CodeValue V ON S.NotificationStatus = V.Value
    JOIN dbo.CodeNamespace X ON X.ID = V.CodeNamespaceID AND X.Name = 'NotificationStatus'
GROUP BY 
    S.SubscriberID
  ,SubscriberName
  ,DaysUntilExpired
  ,S.SubscriptionStatus
  ,SubscriptionStatus

【讨论】：

【解决方案2】：

Sql 抱怨是因为您的 LEFT OUTER JOIN 子查询在列列表中不包含 SubscriberId（并且在 group by 子句中，因为您有一个 COUNT 聚合），因此它无法在此列上进行连接。

你应该这样做：

LEFT OUTER JOIN (SELECT SubscriberID , Count(*) AS NumberUsers FROM dbo.UserInfo GROUP BY SubscriberID ) AS U  
ON S.SubscriberID = U.SubscriberID

【讨论】：