SQL Server Team-based Development - Red Gate Software

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Chapter 6: Reusing T-SQL Code
we run the report. For this purpose, our stored procedure serves the customers' needs
well, and we soon receive a request for a similar report, returning the average sales per
state, for a given month. Note that our new report is required to use the same definition
of "for a given month."
It is very tempting to just copy the existing SelectTotalSalesPerStateForMonth
procedure, and replace sum with avg to meet the new requirements, as shown in
Listing 6-3.
CREATE PROCEDURE dbo.SelectAverageSalesPerStateForMonth
@AsOfDate DATETIME
AS
SELECT AVG(Amount) AS SalesPerState ,
StateCode
FROM dbo.Sales
-- month begins on the first calendar day of the month
WHERE SaleDateTime >= DATEADD(month,
DATEDIFF(month, '19900101',
@AsOfDate),
'19900101')
AND SaleDateTime