Analytics Software

Hi,
I am new to discoverer and i have a doubt. I have a query and within it is a subquery. I want to use a parameter in subquery. The query i want to achive is

select distinct pap.full_name ,papf.payroll_name , pap.employee_number, pap.national_identifier, pap.original_date_of_hire, paf.effective_start_date
from per_all_people_f pap,
per_all_assignments_f paf,
pay_all_payrolls_f papf
where pap.person_id = paf.person_id
and paf.payroll_id = papf.payroll_id
and papf.payroll_name like '%'
and paf.effective_start_date between '01-JAN-2000' and '31-DEC-4712'
and not exists (select paf2.effective_start_date from per_all_assignments_f paf2
where paf2.assignment_id = paf.assignment_id
and paf2.effective_start_date < '01-JAN-2000'
and paf2.payroll_id = paf.payroll_id)


How can i map the paf2.effective_date in the desktop version.

papf.payroll_name and paf.effective_start_date can be mapped using parameters since they are in outer select. how do i do the same for paf2.effective_date

TIA