Обсуждение: Identifying casts

Is there any way of identifying whether a cast was built-in or is
user-defined?

I am tempted to just assume that if the cast is to/from a user-defined
type or uses a user-defined function that it is user-defined.  I suspect
though that a user could define a new cast on pre-defined types using a
pre-defined function.

__
Marc

Hello

you can use oid. When oid is greather than some constant, then cast is
custom. The constant is different on any postgresq versions.

You can get it on clean postgres with statement

select max(oid) from pg_cast;

Regards
Pavel Stehule


On 07/12/2007, Marc Munro <marc@bloodnok.com> wrote:
> Is there any way of identifying whether a cast was built-in or is
> user-defined?
>
> I am tempted to just assume that if the cast is to/from a user-defined
> type or uses a user-defined function that it is user-defined.  I suspect
> though that a user could define a new cast on pre-defined types using a
> pre-defined function.
>
> __
> Marc
>
>

Marc Munro <marc@bloodnok.com> writes:
> Is there any way of identifying whether a cast was built-in or is
> user-defined?

It's not easy.  I'd suggest following the same heuristic pg_dump
does, which is that if any of the source type, target type, or
underlying function is considered user-defined, then the cast is too.

            regards, tom lane