From: Tom Lane <tgl@sss.pgh.pa.us>
To: Daniel Gustafsson <daniel@yesql.se>
cc: Michael Paquier <michael@paquier.xyz>,
        Ayush Tiwari <ayushtiwari.slg01@gmail.com>,
        pgsql-bugs@lists.postgresql.org
Subject: Re: to_date()/to_timestamp() silently accept month=0 and day=0
In-reply-to: <FE1D12FF-7E5D-4ED0-A59F-BEA6DEF7EE2C@yesql.se>
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Comments: In-reply-to Daniel Gustafsson <daniel@yesql.se>
	message dated "Thu, 23 Apr 2026 10:11:47 +0200"
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Date: Thu, 23 Apr 2026 11:40:14 -0400
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Daniel Gustafsson <daniel@yesql.se> writes:
>> On 23 Apr 2026, at 09:57, Michael Paquier <michael@paquier.xyz> wrote:
>> Perhaps we could consider strengthening such inputs on HEAD once v20
>> opens for business?  It would be really a scary thing to backpatch,
>> still a major release is a different thing.

> This could definitely not be backpatched IMO, a quick check in v14 shows=
 the
> same behaviour.  The gregorian calendar goes from BC1 to AD1 and does no=
t
> define a year 0, to_date('0000','YYYY') correctly returns year 0001, han=
dling
> months/days in the same way at least makes it consistent (though I didn'=
t scour
> the archives to see if it was intentionally done like that).

Looking at the code, I think it intentionally interprets zero as
"missing data".  See for example the stanza at formatting.c:4650ff
where tm_mon and tm_mday can be backfilled from a DDD field.

I'm disinclined to change the behavior around this; you're far
more likely to get complaints than kudos.

			regards, tom lane