i have created files for suppliers, products and supplier_products. in the supplier_products file i want to restrict the data to only 1 instance of supplier and product. ie i want to create a combined primary key of the foreign keys supplier_code and product_code.
eg
supplier_a,prod_a
supplier_a,prod_b
supplier_b,prod_a
if the user enters supplier_a,prod_a again i want an error to occurr due to file validation.
if that makes any sense to you i would appreciate your help.