Dynamic row range when calculating moving sum/average using window functions (SQL Server)

Question

I\'m currently working on a sample script which allows me to calculate the sum of the previous two rows and the current row. However, I would like to make the number \'2\' a

Answer 1

You can try something like this which does not use dynamic SQL.

DECLARE @myTable TABLE  (myValue INT)

INSERT INTO @myTable ( myValue ) VALUES  ( 5)
INSERT INTO @myTable ( myValue ) VALUES  ( 6)
INSERT INTO @myTable ( myValue ) VALUES  ( 7)
INSERT INTO @myTable ( myValue ) VALUES  ( 8)
INSERT INTO @myTable ( myValue ) VALUES  ( 9)
INSERT INTO @myTable ( myValue ) VALUES  ( 10)


DECLARE @prev_records INT = 2

;WITH CTE as 
(
SELECT ROW_NUMBER() OVER(ORDER BY myValue) rn,myValue FROM @myTable
)
SELECT (SELECT  SUM(myValue) FROM CTE t2 WHERE t2.rn BETWEEN (t1.rn  - @prev_records) AND t1.rn )
FROM CTE t1

SUM(myValue) OVER() is best option however it does not allow you to pass previous N rows using a variable.