self-referential integrity?

I have two tables and I want to identify (and then delete) rows from the subordinate table that does not have a match in the primary table. eg. Customers (cust_code char(4), name char(20)) Orders (cust_code char(4), ord_date date, etc etc)) So, if a Customer has been deleted, how can I identify (prior to deleting) the orders that do not have a customer record? delete from orders where where orders.cust_code 'does not match any records in the Customer table' This is a simplistic version of events, inactuality my database has about seven levels of lookup; Contracts=>Customers=>Contacts=>Orders=>Order_Lines etc etc I guess what I should be doing is setting up some form of ref. integrity but 1) I don't know how to and 2) I don't know how to I realise that (1) and (2) are the same but I thought that (1) was so important it was worth mentioning twice. ps. I a using Inf 5SE (could be using 7.23SE with a struggle). Mark Webb