Query To get all Employees which has Supervisors only
select ppf.full_name emp_name, ppf1.full_name supervisor_name from per_all_people_f ppf, per_all_assignments_f paaf, per_all_people_f ppf1 where ppf.person_id = paaf.person_id and ppf.employee_number is not null and sysdate between paaf.effective_start_date and paaf.effective_end_date and sysdate between ppf.effective_start_date and ppf.effective_end_date and paaf.supervisor_id = ppf1.person_id