Why cannot you use a SEQUENCE if the SEQUENCE is totally hidden from the application.

the only way to do this in Oracle is:

create sequence emp_seq;
create trigger emp_trigger
before insert on emp for each row
begin
select emp_seq.nextval into :new.empno from dual;
end;
/


The CLIENT will never see or access the sequence. If you are not allowed to use sequences for "portability", then you cannot use identities in SQLServer. In order to implement the SQLServer identity type in Oracle -- the required code is above. Since the client never sees the sequence, never touches it, is not aware of it -- you should (have to) make an exception in this case.

This is as portable as using the proprietary identity type from SQLServer.

If there is some logical reason you cannot use a sequence, submit another question with the reasoning.