From: Tom Lane <tgl@sss.pgh.pa.us>
To: reshkekirill@gmail.com
cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #19023: Table DDL default column expression depending on temp
 objects
In-reply-to: <19023-0a5a85a44ec3f0c6@postgresql.org>
References: <19023-0a5a85a44ec3f0c6@postgresql.org>
Comments: In-reply-to PG Bug reporting form <noreply@postgresql.org>
	message dated "Mon, 18 Aug 2025 13:32:24 -0000"
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Date: Mon, 18 Aug 2025 10:05:55 -0400
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PG Bug reporting form <noreply@postgresql.org> writes:
> I have found two cases when user can define a relation, which has temp
> objects in its DEFAULT expression.
> First example is:
> ```
> reshke=# create temp sequence s1;
> CREATE SEQUENCE
> reshke=# create table tt(i int default nextval('s1'));
> CREATE TABLE
> ```

Appears to me to operate as intended: the DEFAULT will be dropped
at session exit, just as if you'd done DROP SEQUENCE s1 CASCADE.

> I think it is a bug that PostgreSQL allows this DDL to successfully
> complete.

Why?

> reshke=# create temp table  x();
> CREATE TABLE
> reshke=# create table y (i int default nextval('x'));
> CREATE TABLE
> reshke=# insert into y default values ;
> ERROR:  cannot open relation "x"
> DETAIL:  This operation is not supported for tables.

This is not about whether x is temp or not, it's about whether
it's a sequence or not.  The argument of nextval() is declared
as regclass, so we can verify that the constant is the name
of a relation; but the parser has no way to know that it ought
to be a sequence in particular.

> WDYT? Is this indeed a bug?

No.  Sure, in a perfect world we could detect "it's not a sequence" at
parse time, but I can't see inventing "regsequence" just to improve
that.

			regards, tom lane