Re: Time zone specifications, abbreviations vs full names

On Sunday, May 08, 2011 10:23:44 am Christophe Pettus wrote:
> Either I am exceptionally confused, or the documentation in 8.5.3 appears
> to be wrong. Could someone clarify what I'm missing?
>
> The documentation states: "In short, this is the difference between
> abbreviations and full names: abbreviations always represent a fixed
> offset from UTC, whereas most of the full names imply a local
> daylight-savings time rule, and so have two possible UTC offsets." "PST"
> is given as a specific example of an abbreviation in this case. But it
> appears that using "PST" gives you a time zone rule:
>
> CREATE TABLE t (
> z TIMESTAMP WITH TIME ZONE
> );
>
> insert into t values ( '2011-03-13 01:00 PST'::timestamptz);
> insert into t values ( '2011-03-13 01:00-7'::timestamptz );
> update t set z = z + '2 hours'::interval;
>
> select * from t;
> z
> ------------------------
> 2011-03-13 04:00:00-07
> 2011-03-13 03:00:00-07
> (2 rows)
>
> --
>
> But if "PST" really did imply a fixed offset, shouldn't the results be the
> same?

No, PST has an offset of -8. So for your initial entry you have:

test(5432)aklaver=>SELECT z at time zone 'UTC' from t;
timezone
---------------------
2011-03-13 09:00:00
2011-03-13 08:00:00

and after the update:

test(5432)aklaver=>SELECT z at time zone 'UTC' from t;
timezone
---------------------
2011-03-13 11:00:00
2011-03-13 10:00:00

>
> --
> -- Christophe Pettus
> xof(at)thebuild(dot)com

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