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Day of Week function in TSQL

Posted on 2004-04-08
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Last Modified: 2012-06-21
I'm attempting to write a function that will provide me with next day of a given date.  For instance, if the date I have is April 8 2004 (thursday) and I need the first monday following that date.

The problem I've run into is that I can't seem to find a way of detecting what the weekday of a date is.

I've gone this far...

Create Function dbo.GetNextDay(@SDate DateTime, @Day Int)
Returns DateTime
AS
Begin
      Declare @Ret DateTime,
            @DayDif Int

      --HERE I NEED TO SET @DAYDIF TO THE NUMBER OF DAYS BETWEEN THE CURRENT DAY AND THE DAY I'M LOOKING FOR

      Set @Ret = DateAdd(@SDate,@DayDif)

      Return @Ret
End
Go


Thanks in advance.
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Comment
Question by:JackieLee
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9 Comments
 
LVL 6

Expert Comment

by:billy21
ID: 10782411
You use DatePart as so...

select DatePart(dw,'2 nov 2003')
0
 
LVL 6

Expert Comment

by:billy21
ID: 10782423
Also the @@DATEFIRST global tells you the first day of week.  It can be set too

Set @@DATEFIRST = 1 --sets the first day of week to Monday.
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LVL 26

Expert Comment

by:Hilaire
ID: 10782437
this solution works whith any langage settings

--with  @day = 1 for Monday, 2 for Wednesday, and so on through 7 for Sunday.
set @datedif = (15+@day-@@datefirst-datepart(dw, getdate()))%7

Hilaire
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Expert Comment

by:Hilaire
ID: 10782448
Create Function dbo.GetNextDay(@SDate DateTime, @Day Int)
Returns DateTime
AS
Begin
     Declare @Ret DateTime,
          @DayDif Int
     set @DayDif = (15+@day-@@datefirst-datepart(dw, getdate()))%7
     Set @Ret = DateAdd(@SDate,@DayDif)
     Return @Ret
End
Go
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Expert Comment

by:billy21
ID: 10782455
Hilaire,

Should getdate() not be @Sdate?
0
 
LVL 26

Expert Comment

by:Hilaire
ID: 10782459
sorry, tested with getdate(), but I think you need if with @SDate instead

Create Function dbo.GetNextDay(@SDate DateTime, @Day Int)
Returns DateTime
AS
Begin
     Declare @Ret DateTime,
          @DayDif Int
     set @DayDif = (15+@day-@@datefirst-datepart(dw, @SDate))%7
     Set @Ret = DateAdd(@SDate,@DayDif)
     Return @Ret
End
Go
0
 
LVL 26

Expert Comment

by:Hilaire
ID: 10782465
Thanks billy21,
I think ours posts collided ; )
0
 
LVL 26

Accepted Solution

by:
Hilaire earned 250 total points
ID: 10782491
BTW, the whole thing could write

Create Function dbo.GetNextDay(@SDate DateTime, @Day Int)
Returns DateTime
AS
Begin
     Return DateAdd(d, (15+@day-@@datefirst-datepart(dw, @SDate))%7, @SDate)
End
Go

Note I changed the dateadd, the parameters order was wrong and the "d," was missing
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LVL 1

Author Comment

by:JackieLee
ID: 10782501
Thanks Hilaire and Billy.  I chose the more complete/better response.
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