SQL & PL/SQL

Hi

Let's say I have three tables ORDERS, PRODUCT and CLIENT. I want a query that will give me all PRODUCT and CLIENT combinations and the total sum of orders if it has one. If I try to do this:

select P.NAME, C.NAME, SUM(O.AMOUNT)
from PRODUCT P, CLIENT C, ORDER O
where P.ID = O.PRODUCT_ID(+) and
C.ID = O.CLIENT_ID(+)

I get an error where I cannot double outer join a table.

Any ideas?