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From: Tom Lane <[email protected]>
To: jian he <[email protected]>
Cc: Heikki Linnakangas <[email protected]>
Cc: [email protected]
Cc: Chao Li <[email protected]>
Cc: Andrew Dunstan <[email protected]>
Subject: Re: Fix domain fast defaults on empty tables
Date: Mon, 08 Jun 2026 14:12:15 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <CACJufxH+qnnWaySKbJD8pBL5Q+aYFE+hffb6-byT_6uPRB1J2Q@mail.gmail.com>
References: <[email protected]>
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	<CACJufxH+qnnWaySKbJD8pBL5Q+aYFE+hffb6-byT_6uPRB1J2Q@mail.gmail.com>

jian he <[email protected]> writes:
> On Fri, Jun 5, 2026 at 10:08 PM Tom Lane <[email protected]> wrote:
>> 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

Well, that's not great either.  The idea of avoiding evaluating
the default expression altogether when the table is empty could
ameliorate that problem too.

But my point stands: a0b6ef29a introduces different treatment for
domain-CHECK-constraint errors than other types of runtime errors
in the default expression.  I think that is fundamentally the wrong
direction to go in.  We want more consistency here, not less.

			regards, tom lane

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