Web Listing 1: Creation Script for Function fn_workingdays
CREATE FUNCTION dbo.fn_workingdays
(
	@from_dt   AS DATETIME,
	@to_dt     AS DATETIME,
	@datefirst AS INT
) RETURNS INT
AS
BEGIN
	RETURN
	(
		SELECT
			days/7*5 + days%7
				- CASE WHEN 6 BETWEEN from_weekday AND to_weekday
					THEN 1 ELSE 0 END
				- CASE WHEN 7 BETWEEN from_weekday AND to_weekday
					THEN 1 ELSE 0 END
		FROM ( SELECT days, from_weekday,
				from_weekday + days%7 - 1 AS to_weekday
				FROM ( SELECT
			DATEDIFF(day, @from_dt, @to_dt) + 1 AS days,
			DATEPART(weekday, @from_dt + @@DATEFIRST - @datefirst)
			AS from_weekday
		) AS D1
		) AS D2
	);
END
GO