credit card php with order_id

[zeberrun]

for an order id, order comes to checkout_process and order_id is created, order_id takes new number from orders table looking for the

last id. is this process correct?

 

i was creating order_id by using php date ("U") function before, i want to change oscommerce order_id system now (takes the last

auto increment from orders table. meantime if i want this number to be written to the bank credit card system, i create an $order_number with

 

below line, the question is how can i define, select or carry the last customers order_id to this line?

In the $order_number = date("U");

ideas welcome

thx