随笔003：开窗函数

SELECT [SalesOrderID]
      ,[OrderDate]
      ,[CustomerID]
      ,[SalesPersonID]     
      ,[SubTotal]
      ,[TaxAmt]
      ,(SELECT COUNT(*)FROM [AdventureWorks2008R2].[Sales].[SalesOrderHeader] B 
        WHERE A.CustomerID = B.CustomerID) 客户总单数
  FROM [AdventureWorks2008R2].[Sales].[SalesOrderHeader] A
  order by CustomerID,SalesOrderID

SELECT [SalesOrderID]
      ,[OrderDate]
      ,[CustomerID]
      ,[SalesPersonID]     
      ,[SubTotal]
      ,[TaxAmt]
      , COUNT(*) over(partition by customerId) 客户总单数
  FROM [AdventureWorks2008R2].[Sales].[SalesOrderHeader] A
  order by CustomerID,SalesOrderID