public inbox for pgsql-docs@postgresql.org
help / color / mirror / Atom feedFrom: Bruce Momjian <bruce@momjian.us>
To: Dave Cramer <davecramer@postgres.rocks>
Cc: Robert Treat <rob@xzilla.net>
Cc: Kirk Parker <khp@equatoria.us>
Cc: Richard Neill <rjn@richardneill.org>
Cc: github@richardneill.org
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: Please clarify that Timestamp with Timezone doesn't preserve the timezone.
Date: Thu, 14 May 2026 12:39:48 -0400
Message-ID: <agX61I5SYlFJ8pFE@momjian.us> (raw)
In-Reply-To: <CADK3HHJ19ewaV3=491dnEsmSS4_KXn1hXGPfwAumQu1YMy++1A@mail.gmail.com>
References: <177685804902.403059.7237129094698721575@wrigleys.postgresql.org>
<agPDkRGXmdyD1EcR@momjian.us>
<ddf41f033a8add84e1f28a095defafae@richardneill.org>
<agR45nws-Y1StCCH@momjian.us>
<CANwZ8rmZdajKmt1KmTRhO7ex-RUeQNwu7yQw19mWaR08B+BdHA@mail.gmail.com>
<agS4qwKSeb-8CrJc@momjian.us>
<CABV9wwPSTVtyBpe8J2kJ1JA29ZKTVtB3+Wjo2gFLJYWZCbqo-Q@mail.gmail.com>
<agW6gzVtz73ZUjNn@momjian.us>
<CADK3HHJ19ewaV3=491dnEsmSS4_KXn1hXGPfwAumQu1YMy++1A@mail.gmail.com>
On Thu, May 14, 2026 at 08:17:36AM -0400, Dave Cramer 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.
Okay, here is the patch with "conversion".
--
Bruce Momjian <bruce@momjian.us> https://momjian.us
EDB https://enterprisedb.com
Do not let urgent matters crowd out time for investment in the future.
Attachments:
[text/x-diff] time_zone.diff (3.3K, 2-time_zone.diff)
download | inline diff:
diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
index d8d91678e86..9a3b8cfbc1d 100644
--- a/doc/src/sgml/datatype.sgml
+++ b/doc/src/sgml/datatype.sgml
@@ -252,25 +252,25 @@
<row>
<entry><type>time [ (<replaceable>p</replaceable>) ] [ without time zone ]</type></entry>
<entry></entry>
- <entry>time of day (no time zone)</entry>
+ <entry>time of day (no time zone conversion)</entry>
</row>
<row>
<entry><type>time [ (<replaceable>p</replaceable>) ] with time zone</type></entry>
<entry><type>timetz</type></entry>
- <entry>time of day, including time zone</entry>
+ <entry>time of day, including time zone conversion</entry>
</row>
<row>
<entry><type>timestamp [ (<replaceable>p</replaceable>) ] [ without time zone ]</type></entry>
<entry></entry>
- <entry>date and time (no time zone)</entry>
+ <entry>date and time (no time zone conversion)</entry>
</row>
<row>
<entry><type>timestamp [ (<replaceable>p</replaceable>) ] with time zone</type></entry>
<entry><type>timestamptz</type></entry>
- <entry>date and time, including time zone</entry>
+ <entry>date and time, including time zone conversion</entry>
</row>
<row>
@@ -1768,7 +1768,7 @@ SELECT 'abc \153\154\155 \052\251\124'::bytea;
<row>
<entry><type>timestamp [ (<replaceable>p</replaceable>) ] [ without time zone ]</type></entry>
<entry>8 bytes</entry>
- <entry>both date and time (no time zone)</entry>
+ <entry>both date and time (no time zone conversion)</entry>
<entry>4713 BC</entry>
<entry>294276 AD</entry>
<entry>1 microsecond</entry>
@@ -1776,7 +1776,7 @@ SELECT 'abc \153\154\155 \052\251\124'::bytea;
<row>
<entry><type>timestamp [ (<replaceable>p</replaceable>) ] with time zone</type></entry>
<entry>8 bytes</entry>
- <entry>both date and time, with time zone</entry>
+ <entry>both date and time, with time zone conversion</entry>
<entry>4713 BC</entry>
<entry>294276 AD</entry>
<entry>1 microsecond</entry>
@@ -1800,7 +1800,7 @@ SELECT 'abc \153\154\155 \052\251\124'::bytea;
<row>
<entry><type>time [ (<replaceable>p</replaceable>) ] with time zone</type></entry>
<entry>12 bytes</entry>
- <entry>time of day (no date), with time zone</entry>
+ <entry>time of day (no date), with time zone conversion</entry>
<!-- see MAX_TZDISP_HOUR in datatype/timestamp.h -->
<entry>00:00:00+1559</entry>
<entry>24:00:00-1559</entry>
@@ -2263,8 +2263,9 @@ TIMESTAMP WITH TIME ZONE '2004-10-19 10:23:54+02'
then it is assumed to be in the time zone indicated by the system's
<xref linkend="guc-timezone"/> parameter, and is converted to UTC using the
offset for the <varname>timezone</varname> zone.
- In either case, the value is stored internally as UTC, and the
- originally stated or assumed time zone is not retained.
+ In either case, the value is stored internally as UTC. The
+ originally stated or assumed time zone is not retained and
+ <emphasis>cannot</emphasis> be retrieved later.
</para>
<para>
reply
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-docs@postgresql.org
Cc: bruce@momjian.us, davecramer@postgres.rocks, rob@xzilla.net, khp@equatoria.us, rjn@richardneill.org, github@richardneill.org, pgsql-docs@lists.postgresql.org
Subject: Re: Please clarify that Timestamp with Timezone doesn't preserve the timezone.
In-Reply-To: <agX61I5SYlFJ8pFE@momjian.us>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox