"David Monarchi" <david.e.monarchi@gmail.com> writes:
> Looking at some tables, I believe that relfilenode is the the OID of the
> table.
No, OID is the OID of the table.
The clue I think you are missing is that OID is a "system" column, which
basically means that "SELECT *" doesn't show it. But if you do "SELECT
oid,other-fields FROM pg_class" you'll see it.
relfilenode is coincidentally equal to OID in the initial state of a
pg_class entry, but it doesn't necessarily stay that way. If you use
one where you should've used the other, your code will break eventually.
> My problem is that in the pg_class table I don't
> know how to determine which entries are tables.
See relkind.
> And in the pg_attribute
> table I don't know how to determine which of the corresponding rows are
> attributes.
All of them. Depending on what you are doing, you might wish to ignore
system columns (attnum < 0) and/or dropped columns (attisdropped = true).
regards, tom lane