> I want only test in this script if the user is sysdba for disconnect if
> true

In other words, everybody can work with your database except sysdba ?
You don't like sysdbas ? :-)

> I want only accept my defined user that have granted right on
> my database ! except SYSDBA

As was already explained by others, if somebody has full access
to both database file and database server software, you can't expect
any protection of metadata (except some mild security by obscurity).

It is like asking "I have put stamps with message 'Don't touch if you
are not Charles-Henri' on all my belongings, but people still
keeps stealing them. Do you know any *good* stamp manufacturer ?".

Ivan
http://www.volny.cz/iprenosil/interbase/