The day of the week can be retrieved in SQL Server by using the DatePart function. The value returned by function is between 1 (Sunday) and 7 (Saturday). To convert this to a string representing the day of the week, use a CASE statement.
Create function running following script:
CREATE FUNCTION dbo.udf_DayOfWeek(@dtDate DATETIME)
DECLARE @rtDayofWeek VARCHAR(10)
SELECT @rtDayofWeek = CASE DATEPART(weekday,@dtDate)
WHEN 1 THEN 'Sunday'
WHEN 2 THEN 'Monday'
WHEN 3 THEN 'Tuesday'
WHEN 4 THEN 'Wednesday'
WHEN 5 THEN 'Thursday'
WHEN 6 THEN 'Friday'
WHEN 7 THEN 'Saturday'
Call this function like this:
SELECT dbo.udf_DayOfWeek(GETDATE()) AS DayOfWeek
Method 2: (This is update from comments I received below)
SELECT DATENAME(dw, GETDATE())
Reference : Pinal Dave (https://blog.sqlauthority.com)