If you want to show all possible combinations, you would use a Cross Join (also known as a Cartesian Product).
Really, it is the absence of a join, so every record from one table/query is matched up with every record from another table/query.
See: https://support.office.com/en-us/art...1-07061a1478f6
I agree with JoeM, but leave the join between invoices and cust and remove the join between invoices and prod.