To: Thrasher <thrasher@fibers.upc.es>
Cc: Richard Huxton <dev@archonet.com>, pgsql-sql@postgresql.org,
	Thomas Lockhart <lockhart@fourpalms.org>
Subject: Re: Date trunc in UTC 
In-reply-to: <3DDDF4AD.8030105@fibers.upc.es> 
References: <3DDB5991.9060706@fibers.upc.es>
	<200211201306.47345.dev@archonet.com>
	<3DDBAD02.3090406@electronic-group.com>
	<200211211015.42013.dev@archonet.com>
	<11965.1037892419@sss.pgh.pa.us> <3DDDF4AD.8030105@fibers.upc.es>
Comments: In-reply-to Thrasher <thrasher@fibers.upc.es>
	message dated "Fri, 22 Nov 2002 10:11:09 +0100"
Date: Fri, 22 Nov 2002 10:10:42 -0500
Message-ID: <23923.1037977842@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Thrasher <thrasher@fibers.upc.es> writes:
> The biggest point that I see is that it would be nice to have some kind 
> of function that works with UTC values, regarding of which timezone the 
> user has set.

You can do that in 7.3, using the AT TIME ZONE construct.  Observe:

regression-# begin;
BEGIN
regression=# select now();
              now
-------------------------------
 2002-11-22 09:59:48.706508-05			'now' in local time (EST)
(1 row)

regression=# select now() at time zone 'UTC';
          timezone
----------------------------
 2002-11-22 14:59:48.706508			'now' in UTC
(1 row)

regression=# select date_trunc('month', now() at time zone 'UTC');
     date_trunc
---------------------
 2002-11-01 00:00:00				month start in UTC
(1 row)

regression=# select date_trunc('month', now() at time zone 'UTC') at time zone 'UTC';
        timezone
------------------------
 2002-10-31 19:00:00-05				month start in local time
(1 row)

regression=# commit;

This is a tad bulky maybe, but it'd be easy to wrap up in a user-defined
function.

AT TIME ZONE was less functional, and very poorly documented, in 7.2.
The 7.3 version is described at
http://developer.postgresql.org/docs/postgres/functions-datetime.html#FUNCTIONS-DATETIME-ZONECONVERT

			regards, tom lane