sql server - SET DATEFIRST in FUNCTION

Question

I want to SET DATEFIRST in my function but it is not allowed.

SET DATEFIRST 1

I can add the code in a SP and call the SP from the function but I am not keen on doing that.

I can SET the DATEFIRST before I call my function but I am not keen on doing that as well.

Any other work around?

EDIT

Below is the code I want to use in my FUNCTION to return the total working days of the month. But I cant add this code into the FUNCTION because of my DATEFIRST

DECLARE @my int
DECLARE @myDeduct int
DECLARE @day INT
DECLARE @mydate DATETIME
DECLARE @TotalDays INT

SET @mydate = GETDATE()

SET @myDeduct = 0
IF (@@DATEFIRST + DATEPART(DW, @mydate)) % 7 not in (0,1)
SET DateFirst 1 -- Set it monday=1 (value)

--Saturday and Sunday on the first and last day of a month will Deduct 1
IF (DATEPART(weekday,(DATEADD(dd,-(DAY(@mydate)-1),@mydate))) > 5)
SET @myDeduct = @myDeduct + 1

IF (DATEPART(weekday,(DATEADD(dd,-(DAY(DATEADD(mm,1,@mydate))),DATEADD(mm,1,@mydate)))) > 5)
SET @myDeduct = @myDeduct + 1

SET @my = day(DATEADD(dd,-(DAY(DATEADD(mm,1,@mydate))),DATEADD(mm,1,@mydate)))

Set @TotalDays = (select (((@my/7) * 5 + (@my%7)) - @myDeduct))

Select @TotalDays

Answer 1

Instead of

SET DATEFIRST 1

You can do

SELECT (DATEPART(weekday, GETDATE()) + @@DATEFIRST - 2) % 7 + 1