DATEFIRST keyword uses to reset the first day of the week in SQL
Server and @@DATEFIRST returns the current value for the session of DATEFIRST.
For Example:-
As we know SQL Server
set default language US English and SQL Server sets by default DATEFIRST to 7 (Sunday).
SET DATEFIRST 6
If we execute the above query it will set Saturday as the first
day of the week.
@@DATEFIRST, will return the current value of SET DATEFIRST for
the session.
SET LANGUAGE french
GO
SELECT @@DATEFIRST
GO
-- the result will return 1 (Monday)
SET LANGUAGE us_english
GO
SELECT @@DATEFIRST
GO
-- the result will return 7 (Sunday)