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

Question

Post reply

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

wafw1971

SSC Eights!

Points: 976
More actions
March 1, 2013 at 4:40 am

#274732

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)

Viewing 4 posts - 1 through 3 (of 3 total)

You must be logged in to reply to this topic. Login to reply

ChrisM@Work SSC Guru Points: 186127 More actions · Answer 1

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

wafw1971 SSC Eights! Points: 976 More actions · Answer 2

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

ChrisM@Work SSC Guru Points: 186127 More actions · Answer 3

wafw1971 (3/1/2013)
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

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}

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