It all depends on how you have set your planned and developed your solution.
The best way would be to have your customers table, with a unique ID for each customer. Then when your customers place an order you write the order to an 'orders' table, which also contains the unique ID or download path of the products.
That way, when the customer logs in to the customer area of your store you can retrieve the orders for that customer by setting a session variable as the unique customer ID and then using that session variable when querying the orders table (i.e. only pulling back the orders for that customer).
Hope that helps?