教你如何在SQL Server计算列和平均值

SELECT     
Sales.Customer.CustomerID,     
Sales.SalesOrderHeader.SalesOrderID,     
SUM(Sales.SalesOrderDetail.LineTotal) 
AS SubTotalFROM     
Sales.Customer     
INNER JOIN Sales.SalesOrderHeader     
ON Sales.SalesOrderHeader.Customer
ID = Sales.Customer.CustomerID     
INNER JOIN Sales.SalesOrderDetail     
ON Sales.SalesOrderDetail.SalesOrder
ID = Sales.SalesOrderHeader.SalesOrderIDGROUP BY     
Sales.Customer.CustomerID,     
Sales.SalesOrderHeader.SalesOrder
IDHAVING SUM(LineTotal) > 25000.00ORDER BY     
Sales.Customer.CustomerID,     
SalesOrderID ;

SELECT     
Sales.SalesOrderHeader.SalesOrderID,     
AVG(SUM(Sales.SalesOrderDetail.LineTotal)) 
AS AverageFROM     
Sales.SalesOrderHeader     
INNER JOIN Sales.SalesOrderDetail     
ON Sales.SalesOrderDetail.SalesOrder
ID = Sales.SalesOrderHeader.SalesOrder
IDGROUP BY     
Sales.SalesOrderHeader.SalesOrderID

Msg 130, Level 15, State 1, Line 1

Cannot perform an aggregate function on an expression 

containing an aggregate or a subquery.

USE [AdventureWorks]
GO
/****** Object: UserDefinedFunction 
[dbo].[SalesTotals_fnt]   
Script Date: 12/09/2006 11:32:54 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE FUNCTION [dbo].[SalesTotals_fnt]()
RETURNS TABLE
AS RETURN     
(SELECT SalesOrderID, 
SUM(LineTotal)AS TotalSale     
FROM Sales.SalesOrderDetail     
GROUP BY Sales.SalesOrderDetail.SalesOrderID)

CREATE FUNCTION [dbo].[AverageSale_fns] (     
-- Add the parameters for the function here     
-- )RETURNS money
ASBEGIN     
-- Declare the return variable here     
DECLARE @Result money
-- Add the T-SQL statements to compute the return value here     
SET @Result =(SELECTAvg(TotalSale)AS AverageSale     
FROM dbo.SalesTotals_fnt())
-- Return the result of the function     
RETURN @Result
END

DECLARE @Avg moneySELECT @Avg = dbo.AverageSale_fns()
SELECT     *, @Avg as Average,     
TotalSale / @Avg as Ratio,     CASE         
WHEN TotalSale / @Avg > 1 THEN 'Above Average'       
WHEN TotalSale / @Avg < 1 THEN 'Below Average'         
ELSE 'Average'     END
FROM dbo.SalesTotals_fnt()