Add business days to date in SQL without loops

Question

I currently have a function in my SQL database that adds a certain amount of business days to a date, e.g. if you enter a date that is a Thursday and add two days, it will r

Answer 1

CREATE FUNCTION DateAddBusinessDays
(
    @Days int,
    @Date datetime  
)
RETURNS datetime
AS
BEGIN
    DECLARE @DayOfWeek int;

    SET @DayOfWeek = CASE 
                        WHEN @Days < 0 THEN (@@DateFirst + DATEPART(weekday, @Date) - 20) % 7
                        ELSE (@@DateFirst + DATEPART(weekday, @Date) - 2) % 7
                     END;

    IF @DayOfWeek = 6 SET @Days = @Days - 1
    ELSE IF @DayOfWeek = -6 SET @Days = @Days + 1;

    RETURN @Date + @Days + (@Days + @DayOfWeek) / 5 * 2;
END;

This function can add and subtract business days regardless of the value of @@DATEFIRST. To subtract business days use a negative number of days.