Re: 8.5.1. Date/Time Input

On Wed, Sep 9, 2026 at 06:23:24PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/18/datatype-datetime.html
> Description:
>
> Section 8.5.1 says date/time input is accepted "in almost any reasonable
> format, including ISO 8601".
> That holds for years 0001..9999 but not outside them, and I could not find
> the limit stated anywhere.
>
> ISO 8601 writes years outside that range with an explicit sign and more than
> four digits. PostgreSQL
> rejects those, while holding and printing the very same values in its own
> spelling:
>
> SELECT '10000-01-02'::date; -- 10000-01-02
> SELECT '+10000-01-02'::date; -- ERROR: time zone displacement out of
> range: "+10000-01-02"
> SELECT '-0001-01-02'::date; -- ERROR: invalid input syntax for type
> date: "-0001-01-02"
> SELECT '0000-01-02'::date; -- ERROR: date/time field value out of
> range: "0000-01-02"
>
> Per B.1, a token starting with + or - is read as a numeric time zone, and
> the first error names that directly. The negative forms fail differently -
> as plain syntax rather than as a displacement - so I have not assumed the
> same cause for them. Either way, ISO 8601 also counts through a year zero
> where PostgreSQL counts BC from one, so ISO -0001 (2 BC) has no ISO spelling
> PostgreSQL accepts.
>
> I ran into this writing a PostgreSQL driver for Kotlin: for such a year, the
> ISO 8601 that Kotlin's date library produces is a string PostgreSQL will not
> read back — for a date it stores and prints happily.
>
> Suggested wording — qualify the claim rather than describe the parser, e.g.:
>
> "...including ISO 8601 (for years 0001-9999; ISO 8601 expanded years
> carry an explicit sign, which
> is read as a time zone offset — write 10000-01-02 or 0002-01-02 BC
> instead), SQL-compatible,
> traditional POSTGRES, and others."

Good point; for reference:

https://en.wikipedia.org/wiki/ISO_8601#Dates

I have written the attached patch.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

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