I can add six days to a date and get what I expect, but if I add seven days to that same date, I get the same date.
What I mean is this; when the user has enter "12/27/2015" as the value for the @BegDate parameter, this declaration:
DECLARE
@Week1End datetime = DATEADD(Day, 6, @BegDate),
@Week2Begin datetime = DATEADD(Day, 7, @BegDate);
...results in both @Week1End and @Week2Begin being the same date (2016-01-02), as you can see from the result set returned:
This is the TSQL:
CREATE PROCEDURE [dbo].[variancePriceByProductWithPriceChangePercentage]
@Unit varchar(25),
@BegDate datetime,
@EndDate datetime
AS
DECLARE
@Week1End datetime = DATEADD(Day, 6, @BegDate),
@Week2Begin datetime = DATEADD(Day, 7, @BegDate);
Select Ind.Description,
@BegDate BegDate,
@Week1End Week1End,
@Week1End Week2Begin,
@EndDate EndDate,
SUM(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.QtyShipped ELSE 0 END)
Week1Usage,
SUM(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.QtyShipped ELSE 0 END)
Week2Usage,
SUM(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END)
Week1Price,
SUM(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.Price ELSE 0 END) -
SUM(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.QtyShipped ELSE 0 END)
UsageVariance,
SUM(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.QtyShipped ELSE 0 END)
-
SUM(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END)
PriceVariance,
(SUM(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.QtyShipped ELSE 0
END) -
SUM(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END) )
/
NULLIF(SUM(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END),0)
PercentageOfPriceVariance
From InvoiceDetail Ind
Where Ind.Unit = @Unit
AND Ind.InvoiceDate BETWEEN @BegDate AND @EndDate
Group By Ind.Description
So why does @BegDate + 6 equate to the same thing as @BegDate + 7