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From: jian he <jian.universality@gmail.com>
Date: Mon, 8 Jun 2026 08:33:53 +0800
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Subject: Re: Fix domain fast defaults on empty tables
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, pgsql-hackers@lists.postgresql.org,
	Chao Li <li.evan.chao@gmail.com>, Andrew Dunstan <andrew@dunslane.net>
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On Fri, Jun 5, 2026 at 10:08=E2=80=AFPM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Heikki Linnakangas <hlinnaka@iki.fi> writes:
> > On 5 June 2026 10:48:00 EEST, Chao Li <li.evan.chao@gmail.com> wrote:
> >> evantest=3D# create domain d_div as int check (1 / (value - 1) > 0);
> >> CREATE DOMAIN
> >> evantest=3D# create table t (a int);
> >> CREATE TABLE
> >> evantest=3D# alter table t add column b d_div default 1;
> >> ERROR:  division by zero
>
> > It seems totally reasonable to get an error in that case. '1' is not a =
valid value for the datatype, whether or not there are any rows in the tabl=
e.
>
> I think there's reason for concern here, which is that we do not throw
> an error for the apparently equivalent case
>
> regression=3D# create table t2 (a int, b d_div default 1);
> CREATE TABLE
>
> This will give you an error at INSERT, but not CREATE.  So this
> is inconsistent, as well as different from the pre-v19 behavior.
>

However, this is normal behavior for non-domain types.

create table t2 (a numeric default (1::numeric/0.0::float4)); --  ok
alter table t2 add column b numeric default ((1::numeric/0.0::float4)); -- =
error