Re: BUG #6385: extract epoch at timezone returns wrong value

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: sreeraj(at)ordyn(dot)com
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #6385: extract epoch at timezone returns wrong value
Date: 2012-01-08 16:19:18
Message-ID: 5519.1326039558@sss.pgh.pa.us
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sreeraj(at)ordyn(dot)com writes:
> When I give "SELECT extract(epoch from now() );" the output is
> 1325872658.xxx

> I would expect a slightly incremented value when after a few seconds I give
> the command "SELECT extract(epoch from now() at time zone 'utc+05:30');" .
> Nut I get the value 1325833067.xxx which is the value for utc-05:30 !!!

> And when I give "SELECT extract(epoch from now() at time zone
> 'utc-05:30');", I get 1325872672.xxx which is what is expected if I
> specified timezone +05:30 !!!

I think you are confused about the sign convention for time zones
specified in POSIX notation. See
http://www.postgresql.org/docs/9.1/static/datatype-datetime.html#DATATYPE-TIMEZONES
particularly this comment:

Another issue to keep in mind is that in POSIX time zone names,
positive offsets are used for locations west of
Greenwich. Everywhere else, PostgreSQL follows the ISO-8601
convention that positive timezone offsets are east of Greenwich.

This is not a bug, or at least not our bug --- we're just doing the best
we can to cope with inconsistent standards documents.

regards, tom lane

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