From: Tom Lane <tgl@sss.pgh.pa.us>
To: "Watzinger, Alexander" <Alexander.Watzinger@oeaw.ac.at>
cc: "pgsql-general@lists.postgresql.org" <pgsql-general@lists.postgresql.org>
Subject: Re: Support for dates before 4713 BC
In-reply-to: <ca438ff8331c4e109aa1b75a130948ac@oeaw.ac.at>
References: <ca438ff8331c4e109aa1b75a130948ac@oeaw.ac.at>
Comments: In-reply-to "Watzinger, Alexander" <Alexander.Watzinger@oeaw.ac.at>
	message dated "Sat, 20 Aug 2022 14:05:42 -0000"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <4161383.1661105052.1@sss.pgh.pa.us>
Content-Transfer-Encoding: quoted-printable
Date: Sun, 21 Aug 2022 14:04:12 -0400
Message-ID: <4161384.1661105052@sss.pgh.pa.us>
Archived-At: 
 <https://www.postgresql.org/message-id/4161384.1661105052%40sss.pgh.pa.us>
Precedence: bulk

"Watzinger, Alexander" <Alexander.Watzinger@oeaw.ac.at> writes:
> Any chance to add support for dates before 4713 BC? We really would appr=
eciate that.

I'm a little skeptical of the value of applying the Gregorian calendar
before 1582 AD, let alone thousands of years before the Romans invented
anything looking even vaguely like it.

Are you sure there's going to be any point whatsoever in trying to name
individual days that far back?  ISTM you'd be lucky to assign a year
accurately.

> The 4713 BC limit feels very arbitrary, what is the reason for this exac=
t limit?

There are existing equations for calculating Gregorian month/day/year from
Julian day count [1].  They work back to Julian day zero, at least if
you grant that proleptic Gregorian dates are sensible that far back.
Nobody around here has looked into whether they'd work for negative Julian
day numbers (I suspect not though, at least not without work that seems
rather pointless).

			regards, tom lane

[1] https://en.wikipedia.org/wiki/Julian_day