Nested SQL-statements

Question

I'm trying to nest a statement in oracle. The first statement looks like this:
Select DEREF(TREAT (REF(P) AS ref clubmember_ty)).passwd
FROM persons_tab p; This works fine.
This gives me the password from the clubmember_ty. But insted of typing the whole DEREF...statement for every atrribute i want to get, I would like to type something like this:
select cm.username,cm.password,cm.E_mail,cm.surname from(
Select DEREF(TREAT (REF(P) AS ref clubmember_ty))
FROM persons_tab p) cm;
The problem is that i get the error messege: "invalid columname" for cm.username,cm.password,cm.E_mail.
Clubmember is a subtype of person(all created as types) and they are stored in a table that contains types.
Anyone have any suggestions? Thanks.

Answer 1

Could this be done more efficiently with a JOIN? I always think about that when I hear about a situation where one ResultSet is used to drive a query for another. If the first query brings back N records, that means (N+1) network roundtrips to get the final result. That could be a performance killer for large N.
If you can, you're better off writing this as a SELECT with a sub-SELECT or a JOIN.
If you must do it this way, you're always smarter to load the ResultSet into a CachedRowSet or a data structure and then close out the ResultSet right away, IMO.