Using an amemded @From and @To date to get a new result

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Using an amemded @From and @To date to get a new result

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wafw1971

Posted Friday, March 01, 2013 4:40 AM

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Last Login: Tuesday, May 07, 2013 3:30 AM
Points: 62, Visits: 155

This is my criteria for the SQL below:

From Date 07 Jan 2013 To Date 18 Mar 2013

1 - First Sunday After 07 Jan 2013 is 13 Jan 2013 - Done (FirstSunday) 2 - First Sunday Before 18 Mar 2013 is 17 Mar 2013 - Done (LastSunday) 3 - How many days between 13 Jan 2013 and 17 Mar 2013 = 63, Divide 63 by 7 = 9, +1 = 10

So what I need my datediff to do is use the results from the 1st and 2nd rows above (First and Last Sundays date) so I get the correct result for section 3. Can you help?
Declare @From Datetime
Declare @To Datetime

Set @From = '07 Jan 2013'
Set @To = '18 Mar 2013'

Select dateadd(dd, CASE WHEN datepart(weekday, @From) = 1 THEN 0 ELSE 8 - datepart(weekday, @From) END,@From) as FirstSunday,
dateadd(dd, CASE WHEN datepart(weekday, @To) = 1 THEN 0 ELSE 1 - datepart(weekday, @To) END,@To) as LastSunday

,datediff(d,@From, @To)

Post #1425437

ChrisM@Work

Posted Friday, March 01, 2013 6:34 AM

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Points: 5,602, Visits: 10,950

What happens if your initial FROMdate or TOdate happen to be a sunday? This batch shows solutions either way:

-- Recalculating startdate
;WITH SampleData AS (
	SELECT TheDate = CAST('06 Jan 2013' AS DATE) UNION ALL
	SELECT TheDate = '07 Jan 2013' UNION ALL -- StartDate
	SELECT TheDate = '08 Jan 2013' UNION ALL
	SELECT TheDate = '09 Jan 2013' UNION ALL
	SELECT TheDate = '10 Jan 2013' UNION ALL
	SELECT TheDate = '11 Jan 2013' UNION ALL
	SELECT TheDate = '12 Jan 2013' UNION ALL
	SELECT TheDate = '13 Jan 2013' UNION ALL
	SELECT TheDate = '14 Jan 2013' UNION ALL
	SELECT TheDate = '15 Jan 2013' UNION ALL
	SELECT TheDate = '16 Jan 2013' UNION ALL
	SELECT TheDate = '17 Jan 2013' UNION ALL
	SELECT TheDate = '18 Jan 2013' UNION ALL
	SELECT TheDate = '19 Jan 2013' UNION ALL 
	SELECT TheDate = '20 Jan 2013' UNION ALL 
	SELECT TheDate = '21 Jan 2013' 
)
SELECT 
	DATENAME(weekday,TheDate), 
	TheDate, 
	FirstSundayAfterTheDate1 = DATEADD(dd,6-DATEDIFF(dd,7,TheDate)%7,TheDate), -- use this 
	FirstSundayAfterTheDate2 = DATEADD(dd,7-DATEDIFF(dd,6,TheDate)%7,TheDate) -- or this 
FROM SampleData
CROSS APPLY ( -- workings - helps to explain the solution
	SELECT 
		calc1 = DATEDIFF(dd,7,TheDate), 
		calc2 = 6-DATEDIFF(dd,7,TheDate)%7
) x


-- Recalculating enddate
;WITH SampleData AS (
	SELECT TheDate = CAST('06 Mar 2013' AS DATE) UNION ALL
	SELECT TheDate = '07 Mar 2013' UNION ALL 
	SELECT TheDate = '08 Mar 2013' UNION ALL
	SELECT TheDate = '09 Mar 2013' UNION ALL
	SELECT TheDate = '10 Mar 2013' UNION ALL
	SELECT TheDate = '11 Mar 2013' UNION ALL
	SELECT TheDate = '12 Mar 2013' UNION ALL
	SELECT TheDate = '13 Mar 2013' UNION ALL
	SELECT TheDate = '14 Mar 2013' UNION ALL
	SELECT TheDate = '15 Mar 2013' UNION ALL
	SELECT TheDate = '16 Mar 2013' UNION ALL
	SELECT TheDate = '17 Mar 2013' UNION ALL
	SELECT TheDate = '18 Mar 2013' UNION ALL -- enddate
	SELECT TheDate = '19 Mar 2013' UNION ALL 
	SELECT TheDate = '20 Mar 2013' UNION ALL 
	SELECT TheDate = '21 Mar 2013' 
)
SELECT 
	DATENAME(weekday,TheDate), 
	TheDate, 
	calc1 = DATEDIFF(dd,6,TheDate), 
	calc2 = DATEDIFF(dd,6,TheDate)%7,
	LastSundayBeforeEnddate1 = DATEADD(dd,0-DATEDIFF(dd,6,TheDate)%7,TheDate), -- use this
	LastSundayBeforeEnddate2 = DATEADD(dd,-1-DATEDIFF(dd,7,TheDate)%7,TheDate) -- or this
FROM SampleData

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden
Exploring Recursive CTEs by Example Dwain Camps

Post #1425468

wafw1971

Posted Friday, March 01, 2013 8:09 AM

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Group: General Forum Members
Last Login: Tuesday, May 07, 2013 3:30 AM
Points: 62, Visits: 155

Thanks Chris, I have figured it out now:

Declare @From Datetime
Declare @To Datetime

Set @From = '07 Jan 2013'
Set @To = '18 Mar 2013'

SELECT Datediff(Week, dateadd(dd, CASE WHEN datepart(weekday, @From) = 1 THEN 0 ELSE 8 - datepart(weekday, @From) END,@From),
dateadd(dd, CASE WHEN datepart(weekday, @To) = 1 THEN 0 ELSE 1 - datepart(weekday, @To) END,@To))+1

Post #1425532

ChrisM@Work

Posted Friday, March 01, 2013 8:34 AM

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Group: General Forum Members
Last Login: Yesterday @ 8:21 AM
Points: 5,602, Visits: 10,950

wafw1971 (3/1/2013)

Be careful with datepart. From BOL:
"When datepart is week (wk, ww) or weekday (dw), the return value depends on the value that is set by using SET DATEFIRST." The first day of the week is sunday in the US, monday in the UK.

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

Post #1425552

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