SQL Server - SET DATEFIRST and @@DATEFIRST

SELECT * FROM sys.syslanguages

Above query will return resultset(date & language details) as shown in below image:

--@@LANGUAGE will give us the language detail for the current session
--@@DATEFIRST will give us the "first day of a week" value for the current session
--for language 'us_english', default value (first day of a week) = 7
 
SELECT @@LANGUAGE Currentsession_Language
SELECT @@DATEFIRST Defaultvalue_for_usenglish

--to override the default value (first day of a week) = 6 for this current session alone,use SET DATEFIRST
 
SET DATEFIRST 6
SELECT @@DATEFIRST Overriddenvalue_first_day_of_week