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From: Robert Treat <rob@xzilla.net>
Date: Thu, 14 May 2026 14:36:05 -0400
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 <CAJSLCQ0vCaKdUuUue-PXimWPh1_T-_LJzWpOpBCFZyrqWhAUqQ@mail.gmail.com>
Subject: Re: Please clarify that Timestamp with Timezone doesn't preserve the
 timezone.
To: Dave Cramer <davecramer@postgres.rocks>
Cc: Bruce Momjian <bruce@momjian.us>, Kirk Parker <khp@equatoria.us>,
	Richard Neill <rjn@richardneill.org>, github@richardneill.org,
	pgsql-docs@lists.postgresql.org
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On Thu, May 14, 2026 at 8:17=E2=80=AFAM Dave Cramer <davecramer@postgres.ro=
cks> wrote:
> On Thu, 14 May 2026 at 08:05, Bruce Momjian <bruce@momjian.us> wrote:
>> On Thu, May 14, 2026 at 07:57:21AM -0400, Robert Treat wrote:
>> > > I see your point.  I went with adding the wording "no time zone
>> > > adjustment" and "with time zone adjustment" in the table.  Patch
>> > > attached.  You can see the output at:
>> >
>> > The quibble I have with the term "time zone adjustment" is that it
>> > implies there will be some adjustment, but while you can change your
>> > timezone preferences to display a timestamptz value in whatever time
>> > zone you want, the value itself is never adjusted; it is stored as a
>> > universal moment in time that doesn't change, regardless of the window
>> > dressing around it. For this reason I have taken to describing that
>> > difference between the two as that timestamptz stores the date and
>> > time with timezone awareness, and timestamp is date and time with no
>> > timezone awareness. Perhaps that might work better here as well?
>>
>> I used "adjustment" because the value is adjusted on input, and adjusted
>> on output.  I would say the value is not "aware" of the time zone
>> because once it is internally stored as UTC it is no longer aware of the
>> original time zone.
>>
> Adjusted seems like the wrong word. I think the correct word is converted=
.
>

I guess this depends on how you fundamentally think about timestamps
and/or time zones. When you select now(), whether it displays in -04,
+04, or UTC, the time itself is the same time; the time is not
adjusted nor converted, any more than xml or html data changes when
you apply different xslt or css towards it, we just store in one
particular manifestation of itself. The question is, do we store it in
a way where the storage format is cognizant (aka "aware") of the
concept of time zones, like timestamptz, in which case, you can modify
it's display and do timezone related maths in ways that the timezone
without time zone storage format cannot do, because it has no idea of
what a time zone is (ie. it is not aware of time zones as a concept).


Robert Treat
https://xzilla.net