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From: Andrew Dunstan <[email protected]>
To: Tom Lane <[email protected]>
To: Heikki Linnakangas <[email protected]>
Cc: [email protected]
Cc: Chao Li <[email protected]>
Cc: jian he <[email protected]>
Subject: Re: Fix domain fast defaults on empty tables
Date: Sat, 6 Jun 2026 08:41:32 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<[email protected]>


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

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