Query - General - Get records that exist in only in one table and not in other linked tables

I have 3 tables:

1. customer_order c
2. external_customer_order e
3. external_invoice_header h

I want to get all the information in c for the orders that exist in c but do not exist in e and h (key for all records is order_id).

Does anyone has a suggestion about how to do this?

Thanks!

I solved this one with exists:

SELECT *
FROM customer_order c
WHERE NOT EXISTS (SELECT * FROM external_customer_order e WHERE e.order_no = c.order_no)

for some reason my other query with 'NOT IN' didn't work. If anyone can tell me why...be my guest :S

select *
from customer_order c
where c.order_no not in
(select order_no
from external_customer_order)


But problem solved anyway