Create DateFirst in Select - sql

Question

I have a Select Statement that requires that the DateFirst = 1 Monday
In the US so default is 7 Sunday
How can I modify this to embed the DateFirst in the select statement so I can create it as a view?
SET DATEFIRST 1;
SELECT
T_APPLICANT.APPL_ID AS empID,
T_APPLICANT.APPL_LASTNAME,
T_APPLICANT.APPL_FIRSTNAME,
T_APPLICANT_ASSIGNMENT.ASS_STARTDATE,
DATEPART(ww, dbo.T_APPLICANT_ASSIGNMENT.ASS_STARTDATE) AS WeekNo,
DATEPART(WEEKDAY, dbo.T_APPLICANT_ASSIGNMENT.ASS_STARTDATE) AS WeekDay,
DATEPART(ww, GETDATE()) AS CurWeekNo,
(T_APPLICANT_ASSIGNMENT.ASS_HOURS) AS Total_Assigned_hrs,
(T_APPLICANT_ASSIGNMENT.ASS_BILL) AS AvgBill_Rate,
(T_APPLICANT_ASSIGNMENT.ASS_PAY) AS AvgPay_Rate,
(T_APPLICANT_ASSIGNMENT.ASS_HOURS * T_APPLICANT_ASSIGNMENT.ASS_PAY) AS Total_AmtPaid,
(T_APPLICANT_ASSIGNMENT.ASS_HOURS * T_APPLICANT_ASSIGNMENT.ASS_BILL) AS Total_AmtBilled,
(LTRIM(STR(DATEPART(yy, T_APPLICANT_ASSIGNMENT.ASS_STARTDATE))) + '-'
+ LTRIM(STR(DATEPART(M, T_APPLICANT_ASSIGNMENT.ASS_STARTDATE)))
) AS YearMo
FROM
T_APPLICANT
RIGHT OUTER JOIN
T_APPLICANT_ASSIGNMENT
ON T_APPLICANT.APPL_ID = T_APPLICANT_ASSIGNMENT.APPL_ID
WHERE
DATEPART(ww, dbo.T_APPLICANT_ASSIGNMENT.ASS_STARTDATE)
BETWEEN DATEPART(ww, GETDATE()) AND DATEPART(ww, GETDATE()) + 1
AND DATEPART(yy, T_APPLICANT_ASSIGNMENT.ASS_STARTDATE) = DATEPART(yy, GETDATE())
AND ASS_STATUS = 'A';

Answer 1

Unless proven otherwise, you can't set DATEFIRST in a view.
And neither in a user defined function.
So to have a view that returns week & weekday numbers as if DATEFIRST was set to 1?
That could use different calculations.
Haven't figured out yet how to calculate the week number regardless of the DATEFIRST setting as if it the weeks would start on Monday.
That's a tricky one.
I know, one could link to a Calendar table with the week numbers.
But that's not the goal here.
However, the WEEKDAY can also be calculated without using DATEPART.
For example by combining a CASE with a FORMAT.
Because the names of the weekdays remain the same, regardless of the DATEFIRST setting.
And an ISO_WEEK also starts on Monday.
So it can be used in the WHERE clause to filter on the current week & next week.
create table testdatefirst (
id int primary key not null identity(1,1),
dt date not null
)
GO
✓
with rcte as
(
select cast('2018-12-24' as date) dt
union all
select dateadd(day, 1, dt)
from rcte
where dt < cast('2019-03-01' as date)
)
insert into testdatefirst (dt)
select *
from rcte
order by dt
GO
68 rows affected
CREATE view vw_testdatefirst AS
select dt
, FORMAT(dt,'ddd','en-GB') as [dayname]
, DATEPART(WEEKDAY, dt) as [weekday]
, DATEPART(WEEK, dt) as [week]
-- , DATEPART(ISO_WEEK, dt) as [ISO_WEEK]
, case FORMAT(dt,'ddd','en-GB')
when 'Mon' then 1
when 'Tue' then 2
when 'Wed' then 3
when 'Thu' then 4
when 'Fri' then 5
when 'Sat' then 6
when 'Sun' then 7
end as [weekday2]
, (((DATEPART(WEEKDAY, dt) + ##DATEFIRST-2)%7)+1) AS [weekday3]
from testdatefirst
where DATEPART(ISO_WEEK, dt) between DATEPART(ISO_WEEK, '2019-01-01') and DATEPART(ISO_WEEK, '2019-01-01')+1
GO
✓
set datefirst 7;
GO
✓
select ##datefirst as [datefirst];
select * from vw_testdatefirst order by dt;
GO
| datefirst |
| :-------- |
| 7 |
dt | dayname | weekday | week | weekday2 | weekday3
:------------------ | :------ | ------: | ---: | -------: | -------:
31/12/2018 00:00:00 | Mon | 2 | 53 | 1 | 1
01/01/2019 00:00:00 | Tue | 3 | 1 | 2 | 2
02/01/2019 00:00:00 | Wed | 4 | 1 | 3 | 3
03/01/2019 00:00:00 | Thu | 5 | 1 | 4 | 4
04/01/2019 00:00:00 | Fri | 6 | 1 | 5 | 5
05/01/2019 00:00:00 | Sat | 7 | 1 | 6 | 6
06/01/2019 00:00:00 | Sun | 1 | 2 | 7 | 7
07/01/2019 00:00:00 | Mon | 2 | 2 | 1 | 1
08/01/2019 00:00:00 | Tue | 3 | 2 | 2 | 2
09/01/2019 00:00:00 | Wed | 4 | 2 | 3 | 3
10/01/2019 00:00:00 | Thu | 5 | 2 | 4 | 4
11/01/2019 00:00:00 | Fri | 6 | 2 | 5 | 5
12/01/2019 00:00:00 | Sat | 7 | 2 | 6 | 6
13/01/2019 00:00:00 | Sun | 1 | 3 | 7 | 7
set datefirst 1;
GO
✓
select ##datefirst as [datefirst];
select * from vw_testdatefirst order by dt;
GO
| datefirst |
| :-------- |
| 1 |
dt | dayname | weekday | week | weekday2 | weekday3
:------------------ | :------ | ------: | ---: | -------: | -------:
31/12/2018 00:00:00 | Mon | 1 | 53 | 1 | 1
01/01/2019 00:00:00 | Tue | 2 | 1 | 2 | 2
02/01/2019 00:00:00 | Wed | 3 | 1 | 3 | 3
03/01/2019 00:00:00 | Thu | 4 | 1 | 4 | 4
04/01/2019 00:00:00 | Fri | 5 | 1 | 5 | 5
05/01/2019 00:00:00 | Sat | 6 | 1 | 6 | 6
06/01/2019 00:00:00 | Sun | 7 | 1 | 7 | 7
07/01/2019 00:00:00 | Mon | 1 | 2 | 1 | 1
08/01/2019 00:00:00 | Tue | 2 | 2 | 2 | 2
09/01/2019 00:00:00 | Wed | 3 | 2 | 3 | 3
10/01/2019 00:00:00 | Thu | 4 | 2 | 4 | 4
11/01/2019 00:00:00 | Fri | 5 | 2 | 5 | 5
12/01/2019 00:00:00 | Sat | 6 | 2 | 6 | 6
13/01/2019 00:00:00 | Sun | 7 | 2 | 7 | 7
db<>fiddle here