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Problem with DateAdd Function in Query

Posted on 2011-10-13
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Last Modified: 2012-08-14
Today is Oct. 13, 2011 (10/13/11) -

1. The following query will not return any records for 10/12/11 although records do exist:

     SELECT tblProd2.PRID, tblProd2.BsWtAvg, tblProd2.LoftAvg, tblProd2.ProdDate
     FROM tblProd2
     WHERE (tblProd2.ProdDate)=DateAdd("d",-1,Now());

The following queries will work:

     SELECT tblProd2.PRID, tblProd2.BsWtAvg, tblProd2.LoftAvg, tblProd2.ProdDate
     FROM tblProd2
     WHERE (tblProd2.ProdDate)<DateAdd("d",-1,Now());   'Returns all < 10/12/11

     SELECT tblProd2.PRID, tblProd2.BsWtAvg, tblProd2.LoftAvg, tblProd2.ProdDate
     FROM tblProd2
     WHERE (tblProd2.ProdDate)>DateAdd("d",-1,Now());  'Returns all > 10/12/11

     Attempts to use >= or <= in the criteria will not work.

I can use the following to return all records for 10/12/11:

     SELECT tblProd2.PRID, tblProd2.BsWtAvg, tblProd2.LoftAvg, tblProd2.ProdDate
     FROM tblProd2
     WHERE (tblProd2.ProdDate)>DateAdd("d",-2,Now()) AND (tblProd2.ProdDate) < Now());

Why doesn't     WHERE (tblProd2.ProdDate)=DateAdd("d",-1,Now());    return records for 10/12/11?
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Question by:Tim313
6 Comments
 
LVL 120

Expert Comment

by:Rey Obrero (Capricorn1)
ID: 36963387
use Date() instead of Now()

 SELECT tblProd2.PRID, tblProd2.BsWtAvg, tblProd2.LoftAvg, tblProd2.ProdDate
     FROM tblProd2
     WHERE (tblProd2.ProdDate)=DateAdd("d",-1,Date());
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LVL 120

Accepted Solution

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Rey Obrero (Capricorn1) earned 2000 total points
ID: 36963391
the Now() function includes Time values..
0
 
LVL 31

Expert Comment

by:hnasr
ID: 36963902
Why doesn't     WHERE (tblProd2.ProdDate)=DateAdd("d",-1,Now());    return records for 10/12/11?

Using Date() Produces values like 10/12/11
Using Now() Produces values like 10/12/11 09:10:00
Which are not equal
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LVL 26

Expert Comment

by:Nick67
ID: 36965246
Dates are the funnest thing there is!
The previous posters have noted the beginning of the fun--that Date() and Now() do not return the same thing.
One returns 13-Oct-2011 12:00:00 AM and the other returns 13-Oct-2011 02:37:00 PM

That's the start
If tblProd2.ProdDate is filled with values that were based on Now(), they will ALSO have times.
So you can have stuff like Format(tblProd2.ProdDate, "dd-mmm-yyyy") that will return stuff showing today's date.
But it may still fail tblProd2.ProdDate < #13-Oct-2012# because the time part is still there!

Access ALWAYS stores a time.  If you don't specify one (you entered a date by hand -- 13-Oct-2011 or used Date()) then the time is midnight--12:00:00 AM
If you use Now() or specify a time, then the specified time gets stored.

Format() just changes what you SEE for string values, not the actual value of the datetime.
Moreover, your regional settings influence how string-literal times are interpreted.
01/06/11 can be the 6th of January or the 1st of June depending on the settings.

Which is an EXTREMELY good reason NOT to use that format.
ISO 8601 format -- 2011-10-13 -- never gets misinterpreted.
Providing you are always using english, medium date never goes wrong either -- 13-Oct-11

Danger, Will Robinson!  Never forget the time.  It's ALWAYS there

This may play

     SELECT tblProd2.PRID, tblProd2.BsWtAvg, tblProd2.LoftAvg, tblProd2.ProdDate
     FROM tblProd2
     WHERE (tblProd2.ProdDate) >=CDate(Date()-1 & " 11:59:00 PM")
0
 
LVL 52

Expert Comment

by:Gustav Brock
ID: 36969297
It might be a more logical approach to use DateDiff:

WHERE DateDiff("d", tblProd2.ProdDate, Date()) = 1

However, should you have an index on ProdDate, this will not be used.

/gustav
0
 

Author Closing Comment

by:Tim313
ID: 36985371
Thanks to everyone. Since all replies were the same, capricorn1 gets the points for first response.
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