Message-ID: <501C099C.6060904@shopzeus.com>
Date: Fri, 03 Aug 2012 19:25:48 +0200
From: Laszlo Nagy <gandalf@shopzeus.com>
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To: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-admin@postgresql.org
Subject: Re: Messed up time zones
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2012.08.03. 18:38 keltezéssel, Tom Lane írta:
> Laszlo Nagy <gandalf@shopzeus.com> writes:
>> I have intentionally chosen an example where the local time is changed
>> from summer time to winter time (e.g. local time suddenly "goes back"
>> one hour). It demonstrates that you cannot use "at time zone ...."
>> expression to convert a timestamptz into a desired time zone manually.
> Um, yes you can.  The trick is to use a timezone name, not an
> abbreviation, in the AT TIME ZONE construct (for instance,
> 'Europe/Budapest' not just 'CET').  That will do the rotation
> in a DST-aware fashion.
And loose information at the same time. Because after the conversion, 
you won't be able to tell if it is a summer or a winter time. So yes, 
you are right. You can do that kind of conversion, but then sometimes 
you won't know when it was, or what it means. This problem could be 
solved by storing the UTC offset together with the time zone, internally 
in PostgreSQL.

Maybe, if that is not a problem for the user, he can use "at time zone" 
for converting between time zones. Personally, I will stick with UTC and 
use a program to convert values, because I would like to know when it 
was. :-)