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From: H Witt <[email protected]>
To: Bruce Momjian <[email protected]>
Cc: [email protected] <[email protected]>
Subject:  =?gb2312?B?u9i4tDogd2h5IGF0IHRpbWUgem9uZSB0el9vZmZzZXQgbm90IGVxdWFsIHR6?= =?gb2312?B?X25hbWU/ICB0el9uYW1lIGhhcyBzYW1lIG9mZnNldCBpbiBwZ190aW1lem9u?= =?gb2312?Q?e=5Fnames?=
Date: Tue, 29 Apr 2025 06:28:05 +0000
Message-ID: <OSBPR01MB29978241F67EB78F0390C6809B802@OSBPR01MB2997.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <[email protected]>
References: <OSBPR01MB299716C895A69A6DFCF3357C9B812@OSBPR01MB2997.jpnprd01.prod.outlook.com>
	<OSBPR01MB29975FFDA1D860B20A8AC85C9B802@OSBPR01MB2997.jpnprd01.prod.outlook.com>
	<[email protected]>

Hi all,
Thanks for explaining.  I have got it.

________________________________
发件人: Bruce Momjian <[email protected]>
发送时间: 2025年4月29日 11:09
收件人: H Witt <[email protected]>
抄送: [email protected] <[email protected]>
主题: Re: why at time zone tz_offset not equal tz_name? tz_name has same offset in pg_timezone_names

On Tue, Apr 29, 2025 at 02:40:45AM +0000, H Witt wrote:
> select
> '2025-02-03 15:04:05'::timestamptz at time zone '+08:00',
> '2025-02-03 15:04:05'::timestamptz at time zone 'Asia/Shanghai'
>
> display
> |2025-02-02 23:04:05.000|2025-02-03 15:04:05.000|

The sign is wrong in the first column:

        SELECT
        '2025-02-03 15:04:05'::timestamptz at time zone '-08:00',
        '2025-02-03 15:04:05'::timestamptz at time zone 'Asia/Shanghai'
        ;
              timezone       |      timezone
        ---------------------+---------------------
         2025-02-04 04:04:05 | 2025-02-04 04:04:05

See:

        https://www.postgresql.org/docs/current/datetime-posix-timezone-specs.html

        The offset fields specify the hours, and optionally minutes and
        seconds, difference from UTC. They have the format hh[:mm[:ss]]
        optionally with a leading sign (+ or -). The positive sign is used
        for zones west of Greenwich. (Note that this is the opposite of
        the ISO-8601 sign convention used elsewhere in PostgreSQL.) hh
        can have one or two digits; mm and ss (if used) must have two.

--
  Bruce Momjian  <[email protected]>        https://momjian.us
  EDB                                      https://enterprisedb.com

  Do not let urgent matters crowd out time for investment in the future.


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