select a.inv_no, b.account_no, b.location, c.acc_name, d.part_desc ; from order_file a inner join work_history b, work_history b inner ; join customer_billing c, order_file a inner join order_items d; on a.inv_no = b.inv_no into cursor sql_data>>You need to explicit Join all the tables, A with B, B with C, C with D, or whatever relation you have.
SELECT a.inv_no, b.account_no, b.location, c.acc_name, d.part_desc ; FROM order_file a INNER JOIN work_history b ON a.inv_no=b.inv_no ; INNER JOIN customer_billing C ON b.<InnerField> = c.<RelatedField> .... and the next.See in your VFP help the topic "Join Conditions for Tables, Queries, and Views"