paid and unpaid display

hi, have this script that i've been working on, first i have this output that will display all the invoices with corresponding receipt number(or).
now one of the managers wanted also to reflect the unpaid invoices, meaning the invoices may display with or without the receipt number.i've been trying to manipulate the script so i may meet their requirement. any help?

here's my script:

select distinct c.name,it.inv_no,i.coll_date,r.code,r.date_issued
from iteneraries i,receipts r,payments p,customers c,it_invoices it
where i.cust_code=c.code
and i.pcode=c.pcode