Datepart query shows value 1 for saturday - sql

Question

The following is my stored procedure for setting workingday between two dates
Create procedure [dbo].[sp_workingdays](#startdate date,#enddate date,#createddatetime datetime,#adminid int)
as
declare #start date,#end date
declare #day varchar(50)
declare #timeid int
declare #daypare int
declare #workingdaytype varchar(20)
begin
set #start=#startdate
set #end=#enddate
while (#start<=#end)
begin
if #start not in (select Date from Generalholyday_details)
begin
select #day= DATENAME(dw,#start)
select #workingdaytype =case (DATEPART(DW,#start)+##DATEFIRST)%7 when 1 then 'Leave Day' when 2 then 'Full Day' when 3 then 'Full Day' when 4 then 'Full Day'when 5 then 'Full Day' when 6 then 'Full Day' when 0 then 'Half Day' end
select #timeid=Time_id from Workingdaytimesetting_details where Workingday_type=#workingdaytype
insert into Workingday_details(Working_date,working_day,Time_id) values(#start,#day,#timeid)
update Workingday_details set createddatetime=#createddatetime where createddatetime is null
update Workingday_details set adminid=#adminid where adminid is null
end
set #start=DATEADD(day,1,#start)
end
end
GO
In datepart line 1 is for sunday. but actually when i run the stored procedure, i got 1 for Saturday. how can i set 1 for sunday.In my previous system i got 1 for sunday in same procedure.

Answer 1

Have a look at SET DATEFIRST (Transact-SQL)
Sets the first day of the week to a number from 1 through 7.
To see the current setting of SET DATEFIRST, use the ##DATEFIRST
function.
The setting of SET DATEFIRST is set at execute or run time and not at
parse time.
Specifying SET DATEFIRST has no effect on DATEDIFF. DATEDIFF always
uses Sunday as the first day of the week to ensure the function is
deterministic.

Answer 2

Try this one -
SET DATEFIRST 7
DATEFIRST - MSDN
Also try this query after small refactor:
CREATE PROCEDURE [dbo].[sp_workingdays]
(
#startdate DATE
, #enddate DATE
, #createddatetime DATETIME
, #adminid INT
)
AS BEGIN
DECLARE
#start DATE
, #end DATE
, #day VARCHAR(50)
, #timeid INT
, #workingdaytype VARCHAR(20)
SELECT
#start = #startdate
, #end = #enddate
WHILE (#start <= #end) BEGIN
IF NOT EXISTS(
SELECT 1
FROM Generalholyday_details
WHERE #start = [Date]
) BEGIN
SELECT
#day = DATENAME(dw, #start)
, #workingdaytype =
CASE WHEN dt = 1 THEN 'Leave Day'
WHEN dt IN (2,3,4,5,6) THEN 'Full Day'
ELSE 'Half Day'
END
FROM (
SELECT dt = (DATEPART(DW, #start) + ##DATEFIRST) % 7
) t
SELECT #timeid = Time_id
FROM Workingdaytimesetting_details
WHERE Workingday_type = #workingdaytype
INSERT INTO Workingday_details (Working_date, working_day, Time_id)
VALUES (#start, #day, #timeid)
UPDATE Workingday_details
SET createddatetime = #createddatetime
WHERE createddatetime IS NULL
UPDATE Workingday_details
SET adminid = #adminid
WHERE adminid IS NULL
END
SET #start = DATEADD(DAY, 1, #start)
END
END
GO