Re: Behavior of "at time zone"

Hi Adrian,
Thanks for your reply. However, I still don't fully understand why SET TIMEZONE TO and AT TIME ZONE behave differently. Morever the /usr/share/pgsql/timezonesets/America.txt (POSIX) specifies the BRST timezone with a two hour negative offset. Unless I'm missing something the AT TIME ZONE construct is swapping the signs of the offset when specifying the timezone numerically.

Cheers,
Andrew

-----Original Message-----
From: Adrian Klaver [mailto:adrian(dot)klaver(at)gmail(dot)com]
Sent: Friday, 29 January 2010 11:57 AM
To: pgsql-general(at)postgresql(dot)org
Cc: Andrew Crouch
Subject: Re: [GENERAL] Behavior of "at time zone"

On Friday 29 January 2010 5:34:04 am Andrew Crouch wrote:
> Hi there,
> I'm looking to use the "at time zone" language feature,
> however the results below don't really agree with my expectations. Is
> this a bug in 8.4 or am I misinterpreting the results? If it is a
> bug, has it been fixed in the development releases?
>
>
> psql (8.4.0)
> Type "help" for help.
>
> ispdb_br=> set timezone to '-2';
> SET
> ispdb_br=> select now();
> now
> -------------------------------
> 2010-01-29 11:26:22.833697-02
> (1 row)
>
> ispdb_br=> select now() at time zone 'BRST';
> timezone
> ----------------------------
> 2010-01-29 11:26:30.521964
> (1 row)
>
> ispdb_br=> select now() at time zone '-2';
> timezone
> ----------------------------
> 2010-01-29 15:26:47.010222
> (1 row)
>
> ispdb_br=> select now() at time zone '+2';
> timezone
> ---------------------------
> 2010-01-29 11:26:49.55412
> (1 row)

>From here:
http://www.postgresql.org/docs/8.4/interactive/datatype-datetime.html#DATATYPE-TIMEZONES

"One should be wary that the POSIX-style time zone feature can lead to silently accepting bogus input, since there is no check on the reasonableness of the zone abbreviations. For example, SET TIMEZONE TO FOOBAR0 will work, leaving the system effectively using a rather peculiar abbreviation for UTC. 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. "

>
>
> Regards,
> Andrew

--
Adrian Klaver
adrian(dot)klaver(at)gmail(dot)com