Concatenate products in the sequence of their order created date

  Hi Folks,

Could you please help me how to solve below scenario?

We need to concatenate (comma separated) the list of products ordered by a customer.
Conditions here are.

1) Products should be placed in the sequence of their orders. That means, the products which are ordered recently (based on order created date) should be placed first in the concatenated list.

   For Ex:  Prod 1 has ordered first (Order1), then Prod 2 & Prod 3 are ordered in the next order (Order2)

So, in the initial run the concatenated list have the products as; Prod 1, Prod 2, Prod 3.

Next time, if the  same customer has ordered (Order3) for Prod3.This Product3 should be place first in the concatenated list as below:

(Prod3, Prod1, Prod2).

In a nut shell, recently ordered products should appear first in the list,

Kindly help me in resolving this.

Thanks,

  Sam