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DATEADD with milliseconds Expand / Collapse
Posted Thursday, February 19, 2009 8:26 AM


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Last Login: Thursday, June 4, 2009 1:49 PM
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I was hoping that the following code:

declare @end_date as datetime
set @end_date = '2008-03-10 02:00:00.000'
SELECT DATEADD(ms,-1,DATEADD(mm, DATEDIFF(m,0,@end_date)+1,0))

would give me '2008-03-31 23:59:59.999'

but it doesn't, i get '2008-04-01 00:00:00.000'

I think this is because datetime is accurate to roughly 3 milliseconds so it rounds to the next day. If I change it to -2 ms....
SELECT DATEADD(ms,-2,DATEADD(mm, DATEDIFF(m,0,@end_date)+1,0))
I correctly get '2008-03-31 23:59:59.997'

So the question is: How do I accurately determine the last day in the month for a given date, to the last millisecond (999)?
Post #660406
Posted Thursday, February 19, 2009 8:34 AM



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I personally use the 997 milliseconds, otherwise it;'s the next day.
declare @mon datetime,
@fri datetime
@mon =DATEADD(wk, DATEDIFF(wk,0,GETDATE()), 0) ,
@fri =DATEADD(ms,-2,DATEADD(wk, DATEDIFF(wk,0,GETDATE()), 0)+ 5 )

Monday = 2009-02-16 00:00:00.000
Friday = 2009-02-20 00:00:00.000
EODFri = 2009-02-20 23:59:59.997

--so i would use thhoise dates for a BETWEEN command:
SELECT...WHERE SOMEDATE between @mon and @fri


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Post #660423
Posted Thursday, February 19, 2009 8:38 AM



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A lot of it depends on what you are trying to do. If you are accepting dates without time from your users and or are passing them in yourself,
Instead using "columnname between @Start_Date and @EndDate ", You could use columnName >= @Start_Date AND columnName < datetime(d,1,@EndDate)
For the month of January you end up with >= '2009-01-01 00:00:00.000 and < '2009-02-01 00:00:00.000'


Edited to correct things the page stripped out...

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Post #660433
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