Re: Fix domain fast defaults on empty tables

On Fri, Jun 5, 2026 at 10:08 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Heikki Linnakangas <hlinnaka(at)iki(dot)fi> writes:
> > On 5 June 2026 10:48:00 EEST, Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com> wrote:
> >> evantest=# create domain d_div as int check (1 / (value - 1) > 0);
> >> CREATE DOMAIN
> >> evantest=# create table t (a int);
> >> CREATE TABLE
> >> evantest=# 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 table.
>
> I think there's reason for concern here, which is that we do not throw
> an error for the apparently equivalent case
>
> regression=# 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