Purchase Interface Topic (Not Important)

One of the things I am interested in as far as order processing systems go is how they handle multiples of the same item. The below image, I think illustrates the problem of containing multiples within the product table. The interface just displays the state of the table: a multiple of single line items of the same thing. Instead of the interface saying, okay, we have x number of this type at this size, it says, this line on the database says this number of this type and this size and this line of the database says . . . and so on and so on. This is good because the interface is flexible: a user can either use the count box to increment up the number of pictures ordered or just click on the "add print" button. Additionally, the user is able to add a different type or size of the same print (in two steps). However, if the user uses this for the former rather than for the latter, the user has to count up the number of items manually. Further, if the product fulfillment table looks like the interface, it would be more difficult to generate sales statistics.