在多个表上的SQL LEFT JOIN

Question

给定三个表：

1. Account
   1. UniqueID
   2. Account Group
2. VR
   1. UniqueID
   2. AccountID
3. CR
   1. UniqueID
   2. AccountID

在VR和CR找到的AccountID引用Account的UniqueID 。

我想以获得结果，其示出了我的Account的组Account中的第一列和每数据量Account组的VR在第二列和最后的每数据量Account组中柱3形式CR 。

实现这种连接的正确方法是什么？

我的尝试：

SELECT account_group AS 'Account Group',
  COUNT(Account.AccountId) AS 'Anzahl Accounts',
  COUNT(VR.ActivityId) AS 'VR',
  COUNT(Contact.ContactId) AS 'Contact'
  FROM [MSCRM].[dbo].[AccountBase]
  LEFT JOIN MSCRM.dbo.visit_report_activityBase
    ON Account.AccountId = VR.account_id
  LEFT JOIN MSCRM.dbo.ContactBase
    ON Account.AccountId = Contact.ParentCustomerId
  GROUP BY account_group
  ORDER BY account_group ASC;

但是没有COUNT(*)显示我想要的实际金额。

即使是COUNT的Account.AccountId表示无效号码。

Answer 1

我相信您正在寻找的东西与众不同：

SELECT account_group as 'Account Group',
       count(distinct Account.AccountId) as 'Anzahl Accounts',
       count(distinct VR.ActivityId) as 'VR' count(distinct Contact.ContactId) as 'Contact'
  FROM [ MSCRM ] . [ dbo ] . [ AccountBase ] as Account
  left join MSCRM.dbo.visit_report_activityBase as VR
    on Account.AccountId = VR.account_id
  left join MSCRM.dbo.ContactBase as Contact
    on Account.AccountId = Contact.ParentCustomerId
 group by account_group
 order by account_group