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

If possible dispersion of the range variable is not very high, you can use simple CASE statement to switch between calculations

DECLARE @myTable TABLE  (myValue INT)

-- let's say it could be between 1 and 10
DECLARE @range int = 3;

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)

SELECT 
    CASE @range
        WHEN 1 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 1 PRECEDING AND CURRENT ROW)
        WHEN 2 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 2 PRECEDING AND CURRENT ROW)
        WHEN 3 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 3 PRECEDING AND CURRENT ROW)
        WHEN 4 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 4 PRECEDING AND CURRENT ROW)
        WHEN 5 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 5 PRECEDING AND CURRENT ROW)
        WHEN 6 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 6 PRECEDING AND CURRENT ROW)
        WHEN 7 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 7 PRECEDING AND CURRENT ROW)
        WHEN 8 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 8 PRECEDING AND CURRENT ROW)
        WHEN 9 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 9 PRECEDING AND CURRENT ROW)
        WHEN 10 THEN SUM(myValue) OVER (ORDER BY myValue ROWS BETWEEN 10 PRECEDING AND CURRENT ROW)
    END
FROM @myTable