not sure i understand your question and now that i reread you post I am not sure my answer will work as you have likley have vendors associated to multiple AP records.
my example was how to handle something like this
table_A (clients)
table_B (client_balance)
link A to B as an outer join on clientid
not all clients have made a client balance
I want to see all clients with a zero balance or no balance (e.g. not in table b)
your select statement would be
isnull(table_B.balance) or table.balance = 0
You might need to explain your join and row level data in each table a little it more.
Usually you have to do what you want (if I am understanding better now) using a different source type like a sql store procedure/view (or its equivalent in your data type) or a crystal command. Or you have to suppress rows of data rather than exclude them.