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DATEADD Off By An Hour

Posted on 2014-09-18
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Last Modified: 2014-09-19
Hello:

One of the fields I have in a report is based on the following T-SQL query:

DATEADD(s,({*Document_tb:TimeCreated} + (3600*-5)),'1/1/1970')

The customer is saying that the resulting "Time Created" is off by an hour.  Specifically, this field displayed as 2:24 PM, when it should have displayed as 3:24 PM.

The customer is in the Eastern Time Zone.  It is possible, too, that this field is not changing with the Daylight Savings Time change occurring in the spring.  

Anyway, to manually fix this, do I change the -5 to a different number such as -4 or -6?

TBSupport
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Question by:TBSupport
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Accepted Solution

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Kent Olsen earned 500 total points
ID: 40331539
Hi TBSupport,

It looks like the code is converting from GMT to EST.  

Change -5 to -4.

And note that this kind of conversion may have other issues down the line....
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Expert Comment

by:ste5an
ID: 40331542
First of all: get rid of the unnecessary calculus. Use DATEADD(HOUR,{},'') instead. Your time created value must be an integer value. So when this is a time value, then the problem maybe the implicit conversion from your time value to INT. Maybe DATEADD(HOUR, -5, {}) is sufficient.
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Expert Comment

by:Scott Pletcher
ID: 40331630
>> It is possible, too, that this field is not changing with the Daylight Savings Time change occurring in the spring. <<

I strongly suspect that's it.  Nasty, because then you need a table for DST so you can tell if the setting is different now vs. when the document was created.  But I think you'll need that to accurately translate these times.
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Expert Comment

by:PortletPaul
ID: 40331947
Appears that the field value is a Unix timestamp (expressed as seconds from 1970-01-01) hence the arithmetic requiring 3600*-5 :: and I don't believe there is an implicit conversion, just adding seconds to a date.

alternate: put time out with EST as suffix (i.e. don't attempt daylight saving conformance)

i.e.
this field displays as 2:24 PM EST

(and it won't display 3:24 PM ESST)

----
or whatever your summer time TZ abbreviation is
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