Обсуждение: BUG #19023: Table DDL default column expression depending on temp objects

The following bug has been logged on the website:

Bug reference:      19023
Logged by:          Kirill Reshke
Email address:      reshkekirill@gmail.com
PostgreSQL version: 18beta3
Operating system:   any
Description:

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
```
I think it is a bug that PostgreSQL allows this DDL to successfully
complete. There is a validation for this type of DDL already, example:
```
reshke=# create table ttx(i int default nextval('s3'));
ERROR:  relation "s3" does not exist
LINE 1: create table ttx(i int default nextval('s3'));
                                               ^

```

Since PostgreSQL already checks for its nextval() input, we can teach server
to also validate relation relpersistence, arent we?

Second example is with tables:
```
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.

```

WDYT? Is this indeed a bug?

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