Date: Fri, 18 Sep 2026 11:48:53 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Kacper Kuras <kacperkuras@hotmail.com>
Cc: "pgsql-docs@lists.postgresql.org" <pgsql-docs@lists.postgresql.org>
Subject: Re: 8.5.1. Date/Time Input
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On Fri, Sep 18, 2026 at 02:50:20PM +0000, Kacper Kuras wrote:
> Thanks. In the patch, "without a sign" only holds for years after
> 9999: dropping the minus from -0001-01-02 gives 0001-01-02, which is
> 1 AD, not 2 BC. Perhaps:
> 
>     (ISO 8601 writes years after 9999 with a leading plus sign, and
>     years before 1 AD from a year zero, so 0000 is 1 BC and -0001 is
>     2 BC.  PostgreSQL accepts neither; write 10000-01-02 and
>     0002-01-02 BC instead.)

Looking at the wiki page again, I see:

	To represent years before 0000 or after 9999, the standard also
	permits the expansion of the year representation but only by prior
	agreement between the sender and the receiver.[25] An expanded
	year representation [±YYYYY] must have an agreed-upon number of
	extra year digits beyond the four-digit minimum, and it must be
	prefixed with a + or - sign[26] instead of the more common AD/BC
	(or CE/BCE) notation; by convention 1 BC is labelled +0000,
	2 BC is labeled -0001, and so on.[27]

The "agreement between the sender and the receiver" makes it seem we
don't need to document that we don't support signs on the years.

-- 
  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.