On 2026-06-05 Fr 10:08 AM, Tom Lane wrote:
Heikki Linnakangas<[email protected]> writes:
On 5 June 2026 10:48:00 EEST, Chao Li<[email protected]> 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.
Concretely, I'm pretty sure it is a hazard for pg_dump, which thinks
it can freely transform bits of CREATE operations into ALTERs.
I didn't try to make an example case, but I suspect it is now possible
to create a database that will fail dump/restore because of this
inconsistency.
Seems reasonable. So which of Chao's solutions do you prefer? I think
both will meet the pg_dump issue, not sure how much we care about the
case where we have deleted all the rows but not truncated the table.
cheers
andrew
--
Andrew Dunstan
EDB: https://www.enterprisedb.com
