To: kenzoid@io.com
Cc: pgsql-sql@postgresql.org
Subject: Re: Timezone issue with date_part 
In-reply-to: <20021102065654.GA8564@roark.kenzoid.com> 
References: <20021102065654.GA8564@roark.kenzoid.com>
Comments: In-reply-to Ken Kennedy <kkennedy@kenzoid.com>
	message dated "Sat, 02 Nov 2002 01:56:54 -0500"
Date: Sat, 02 Nov 2002 09:17:14 -0500
Message-ID: <20169.1036246634@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Ken Kennedy <kkennedy@kenzoid.com> writes:
> [ date_part('epoch') is wrong for a timestamp value ]

The epoch value is really only correct for a TIMESTAMP WITH TIME ZONE
value.  If you apply date_part('epoch') to a timestamp without time zone,
as you appear to be doing here, what you will get is the epoch for the
given value interpreted as GMT.

A hack solution is to cast the value to TIMESTAMP WITH TIME ZONE before
extracting the epoch; the cast will assume that the given value is local
time.  But a better idea is to store the column as TIMESTAMP WITH TIME
ZONE in the first place.

(IMHO, the SQL spec is really brain-dead to define timestamp without
time zone as the default form of timestamp; the variant with time zone
is much more useful for most applications.  It's far too easy to shoot
yourself in the foot when working with zoneless timestamps --- usually
in a way that you won't notice until daylight-savings transition time
comes around, or you roll out the app to users in other time zones.)

			regards, tom lane