SELECT @@DATEFIRST ile tanımlı değeri alabiliriz
SET DATEFIRST 1 (İlk günü Pazartesi olarak tanımlayabiliriz)

CREATE FUNCTION DayOfWeek(@date DATETIME)
RETURNS VARCHAR(9)
AS
BEGIN
DECLARE @defDayofWeek VARCHAR(10)
DECLARE @dofWeek int
SET @dofWeek= (@@DATEFIRST + DATEPART(weekday,@Date)-1)%7
SELECT @defDayofWeek=CASE @dofWeek
WHEN 0 THEN ‘Pazar’
WHEN 1 THEN ‘Pazartesi’
WHEN 2 THEN ‘Salı’
WHEN 3 THEN ‘Çarşamba’
WHEN 4 THEN ‘Perşembe’
WHEN 5 THEN ‘Cuma’
WHEN 6 THEN ‘Cumartesi’
END
RETURN (@defDayofWeek)
END

Harun Pekşen