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

问题

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 ?

回答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

回答2:

Just set in query

SET DATEFIRST 1;

Value First day of the week is 1 Monday 2 Tuesday 3 Wednesday 4 Thursday 5 Friday 6 Saturday 7 (default, U.S. English) Sunday

回答3:

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')

回答4:

A horrible situation....Say you are using a shared server and apps can get moved around to different servers based on loads and for some reason one server was setup with a different firstDate for another application....and you are returning the week day in a table function (ie can't set firstdate in this function). This will always guarantee Monday as the first day.

CREATE FUNCTION fnGetMondayWD(@WD INT)
RETURNS INT
AS
     BEGIN

         /* think of 1 to 7 as a clock that can rotate forwards or backwards */

         DECLARE @OFFSET INT, @calc INT;
         SET @offset = @@DATEFIRST + @WD - 1;--Monday DateFirst
         SET @calc = IIF(@offset > 7, @offset - 7, @offset); -- could be @offset % 7 (less readable more efficient)
         RETURN @calc;
     END;

go

-- Test Cases


SET datefirst 7
select dbo.fnGetMondayWD(2) Mon,
     dbo.fnGetMondayWD(3)Tue, 
     dbo.fnGetMondayWD(4)Wed, 
     dbo.fnGetMondayWD(5)Thur, 
     dbo.fnGetMondayWD(6)Fri, 
     dbo.fnGetMondayWD(7)Sat, 
     dbo.fnGetMondayWD(1)Sun


SET datefirst 6
select dbo.fnGetMondayWD(3) Mon,
     dbo.fnGetMondayWD(4)Tue, 
     dbo.fnGetMondayWD(5)Wed, 
     dbo.fnGetMondayWD(6)Thur, 
     dbo.fnGetMondayWD(7)Fri, 
     dbo.fnGetMondayWD(1)Sat, 
     dbo.fnGetMondayWD(2)Sun

SET datefirst 5
select dbo.fnGetMondayWD(4) Mon,
     dbo.fnGetMondayWD(5)Tue, 
     dbo.fnGetMondayWD(6)Wed, 
     dbo.fnGetMondayWD(7)Thur, 
     dbo.fnGetMondayWD(1)Fri, 
     dbo.fnGetMondayWD(2)Sat, 
     dbo.fnGetMondayWD(3)Sun

SET datefirst 1
select dbo.fnGetMondayWD(1) Mon,
     dbo.fnGetMondayWD(2)Tue, 
     dbo.fnGetMondayWD(3)Wed, 
     dbo.fnGetMondayWD(4)Thur, 
     dbo.fnGetMondayWD(5)Fri, 
     dbo.fnGetMondayWD(6)Sat, 
     dbo.fnGetMondayWD(7)Sun

来源：https://stackoverflow.com/questions/20031802/how-to-set-monday-as-first-day-of-week-in-sql-server

标签

sql-server

sql-server-2008

dayofweek