How to set monday as first day of week in SQL Server

Question

I am running SQL Server 2008 on a machine with regional settings that have Monday as the first day of the week. If I create a computed column in a table to compute the day of week for a date field then I get 2 for a Monday date instead of 1.

Is there some property for the table or database or server that I need to set ?

Answer 1

The first day of the week is based on your language settings of the server. The default setting for us_english is 7 (Sunday)

You can find the current first day of the week by using SELECT @@DATEFIRST

---

However, you can use DATEFIRST for this. Just put it at the top of your query

SET DATEFIRST 1; this sets Monday to the first day of the week for the current connection.

http://technet.microsoft.com/en-us/library/ms181598.aspx

Answer 2

You can use DATEPART(dw, GETDATE()) but be aware that the result will rely on SQL server setting @@DATEFIRST value which is the first day of week setting (In Europe default value 7 which is Sunday).

Alternative way is to explicitly specify the first day of week value as parameter and avoid depending on @@DATEFIRST setting. You can use the following formula to achieve that when need it:

(DATEPART(dw, GETDATE()) + @@DATEFIRST + 6 - @WeekStartDay) % 7 + 1

where @WeekStartDay is the first day of the week you want for your system (from 1 to 7 which means from Monday to Sunday).

I have wrapped it into below function so we can reuse it easily:

CREATE FUNCTION [dbo].[GetDayInWeek](@InputDateTime DATETIME, @WeekStartDay INT)
RETURNS INT
AS
BEGIN
    --Note: @WeekStartDay is number from [1 - 7] which is from Monday to Sunday
    RETURN (DATEPART(dw, @InputDateTime) + @@DATEFIRST + 6 - @WeekStartDay) % 7 + 1 
END

Example usage: GetDayInWeek('2019-02-04 00:00:00', 1)

It is equivalent to following (but independent to DATEFIRST setting):

SET DATEFIRST 1
DATEPART(dw, '2019-02-04 00:00:00')