Re: Should we document how column DEFAULT expressions work?

David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> On Wed, 26 Jun 2024 at 17:12, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Do we want to do anything about
>> nextval()? I guess if you hold your head at the correct
>> angle, that's also a magic-input-value issue, in the sense
>> that the question is when does regclass input get resolved.

> I think I'm not understanding what's special about that. Aren't
> 'now'::timestamp and 'seq_name'::regclass are just casts that are
> evaluated during parse time in transformExpr()?

Right. But there is an example in the manual explaining how
these two things act differently:

'seq_name'::regclass
'seq_name'::text::regclass

The latter produces a constant of type text with a run-time
cast to regclass (and hence a run-time pg_class lookup).
IIRC, we document that mainly because the latter provides a way
to duplicate nextval()'s old behavior of run-time lookup.

Now that I think about it, there's a very parallel difference in
the behavior of

'now'::timestamp
'now'::text::timestamp

but I doubt that that example is shown anywhere.

regards, tom lane