Calculate weekend

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Calculate weekend

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Lynn Pettis

Posted Sunday, December 02, 2012 8:54 AM

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Another question, startdate is 2012-12-02 (a Sunday) and you add 1 day, do you want 2012-12-03 or 2012-12-04? What if you add 0 days to the same date? Will you every add a negative number of days (i.e. go backwards from a given date)?

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Lynn Pettis

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Post #1391732

kapil_kk

Posted Monday, December 03, 2012 3:21 AM

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in this case it will be '2012-02-03'

Post #1391827

kapil_kk

Posted Monday, December 03, 2012 3:22 AM

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I have created this script but looking for more optimization regarding performance--

DECLARE @count int
SET @count = 30
DECLARE @sundays int
SET @sundays = 0
DECLARE @startdate datetime
SET @startdate ='2012-01-01'
DECLARE @enddate datetime
SET @enddate = DATEADD(DD,@count,@startdate)
PRINT @enddate
PRINT 'Before Sunday'
WHILE @startdate <= @enddate
BEGIN
IF DATEPART(DW,@startdate) = 1
BEGIN
SET @sundays = @sundays + 1
SET @enddate = DATEADD(DD,1,@enddate)
PRINT @enddate
PRINT 'After Sunday'
PRINT @sundays
END
SET @startdate = DATEADD(DD,1,@startdate)
END

Post #1391829

Jason-299789

Posted Monday, December 03, 2012 3:51 AM

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Using a Tally Table would improve this code significantly, also you have to be careful about using the fucntion datepart(dw,a_date) as in some cases Sunday isnt always represented by 1, and will depend on your regional settings.

Eg : In the US, DW 1 is Sunday, yet in europe it can be DW 1 is monday.

See books on line http://msdn.microsoft.com/en-us/library/ms174420.aspx

To mitigate this you need to use the SET DATEFIRST to make it consistent across all regional settings, see http://msdn.microsoft.com/en-us/library/ms181598.aspx

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Post #1391836

Pete Cox

Posted Monday, December 03, 2012 5:45 AM

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Anyone know if Joe's query

SELECT (C2.julian_business_nbr - C1.julian_business_nbr)
FROM Calendar AS C1, Calendar AS C2
WHERE C1.cal_date = '2007-04-05',
AND C2.cal_date = '2007-04-10';

causes a cross join before the complete WHERE clause is applied ?

Or are we just cross joining the 2 rows that would be the answer sets of 2 discreet queries, each using one of the phrases of the where clause?

Post #1391871

Jeff Moden

Posted Monday, December 03, 2012 5:49 AM

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Jason-299789 (12/3/2012)

Jason,

I know it sounds strange to those of us that use a Tally Table on a regular basis, but there are still a lot of folks that don't know what it is. You either have to explain, provide a link, or provide the full code (preferably some combination of those) for people that don't understand.

--Jeff Moden

"RBAR is pronounced "ree-bar" and is a "Modenism" for "Row-By-Agonizing-Row".

First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column."

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Post #1391875

kapil_kk

Posted Monday, December 03, 2012 5:51 AM

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Jeff is right...
I dont have any knowledge of Tally Table..

Post #1391878

Jeff Moden

Posted Monday, December 03, 2012 5:58 AM

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kapil_kk (12/3/2012)

Jeff is right...
I dont have any knowledge of Tally Table..

Please see the following article. A Tally Table (or Numbers table, as some call it) is a simple table of sequential integers used to replace a WHILE loop.
http://www.sqlservercentral.com/articles/T-SQL/62867/

Joe is correct though. A Calendar table (pretty obvious what that is) would do better here. I'm on my way to work so don't have the time to demo that kind of solution now but I'll check on this post when I get home.

--Jeff Moden

Post #1391884

Pete Cox

Posted Monday, December 03, 2012 6:09 AM

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Using Joe's Calendar table, this might provide a way for the kapil to get to the answer he wants.
It removes the need to recursively check if you added another sunday in the extension of the date period

SELECT cal_date FROM Calendar
WHERE julian_business_nbr = (SELECT julian_business_nbr + 30 FROM Calendar WHERE cal_date = '2007-04-05')

Post #1391892

bleroy

Posted Monday, December 03, 2012 6:51 AM

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I'm with CELKO - use a calendar table, then you can count your Sundays, weekends, Easter Mondays and whatever else you need between two dates - much much easier, and kind on processing too.

For an example calendar, you can check out:
http://www.kimballgroup.com/data-warehouse-and-business-intelligence-resources/data-warehouse-books/booksmdwt/ (go to Chapter 7—Design and Develop the ETL System; date dimension) - Direct Link for DDL and sample data:
http://www.kimballgroup.com/wp-content/uploads/2012/07/Ch07_Date_Dim_2000-2020.xlsx

HTH,

B

Post #1391915

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