-- Sample Data
DECLARE @Foo TABLE (dptNO INT, saleDAY DATE, prodMONTH INT, QUANTITY INT)
INSERT @Foo VALUES
(50763, '02/01/12', 201302,309527),
(50763, '02/02/12', 201302,308888),
(50763, '02/03/12', 201302,303204),
(50763, '02/04/12', 201302,303203),
(50763, '02/05/12', 201302,300604),
(50763, '02/05/12', 201302,300127),
(50763, '02/07/12', 201302,299101),
(50763, '02/08/12', 201302,298966),
(50763, '02/09/12', 201302,296425),
(50763, '02/10/12', 201302,294471),
(50763, '02/11/12', 201302,294161),
(50763, '02/12/12', 201302,294159),
(50763, '02/13/12', 201302,293028),
(50763, '02/14/12', 201302,292034),
(50763, '02/15/12', 201302,291794),
(50763, '02/16/12', 201302,288485),
(50763, '02/17/12', 201302,288485),
(50763, '02/18/12', 201302,288485),
(50763, '02/05/12', 201302,287777),
(50763, '02/20/12', 201302,287732),
(50763, '02/21/12', 201302,287365),
(50763, '02/22/12', 201302,286684),
(50763, '02/23/12', 201302,286363),
(50763, '02/24/12', 201302,285396),
(50763, '02/25/12', 201302,284575),
(50763, '02/26/12', 201302,284575),
(50763, '02/27/12', 201302,284575),
(50763, '02/28/12', 201302,284187)


-- Query
;WITH Cte
AS
(
	SELECT
		saleDAY,
		SUM(QUANTITY) AS QUANTITY,
		ROW_NUMBER() OVER (ORDER BY SaleDay) AS RowNum
	FROM 
		@Foo
	GROUP BY
		SaleDay

)
SELECT
	A.saleDAY,
	A.Quantity + B.Quantity + C.Quantity
FROM
	Cte AS A
INNER JOIN
	Cte AS B
	ON A.RowNum = B.RowNum + 1
INNER JOIN
	Cte AS C
	ON A.RowNum = C.RowNum + 2
ORDER BY
	A.Quantity + B.Quantity + C.Quantity DESC

8/1/2013			8/2/2013			8/3/2013	
Dept. 50763	540	Dept. 50763	213	Dept. 50763	260
Item1	72		Item1	58		Item1	69
Item2	81		Item2	67		Item2	79
Item3	55		Item3	40		Item3	50
Item4	62		Item4	48		Item4	62
							
5/15/2013		5/16/2013		5/17/2013	
Dept. 50764	514	Dept. 50764	450	Dept. 50764	430
Item1	186		Item1	175		Item1	159
Item2	104		Item2	92		Item2	114
Item3	113		Item3	101		Item3	70
Item4	60		Item4	48		Item4	64
Item5	46		Item5	34		Item5	21
Item6	5		Item6	0		Item6	2