SQL求助

Question 1:
You are provided with a data table containing customer order IDs, customer IDs, the date each order was placed, product IDs of the products contained in the order, and the quantity ordered.  A sample table in comma-separated format would look as follows:

Order_id, Customer_id, order_date, Product_id, Quantity
O1,C1,01-Jan-2012,P1,10
O2,C2,01-Jan-2014,P2,15
O3,C3,01-Apr-2014,P3,17
O4,C4,01-Apr-2015,P1,20
O5,C4,01-Jan-2016,P2,1
O6,C1,01-May-2013,P5,7
…

We would like to identify customers who have begun to reduce the number of items they purchase online, so that we can target them with a new advertising campaign intended to rekindle their interest in shopping.

(1)        Use a programming language of your choice to identify customers whose order quantities are decreasing. Specifically, we are interested in customers that display an ordering pattern where the total order quantity of their n-th order is less than that of their (n-1)-th order, and the total order quantity of their (n-1)-th order is less than that of their (n-2)-th order, where the n-th order represents that customer’s most recent order.

.. Then the query displays table with the quantity from most recent order to oldest order group by each customer. If the pattern of decreasing is discovered, then these customers are identified.

(2)        How would you change the logic given above in (1) to better identify customers who are appropriate for this advertising campaign?  Justify your new logic and rewrite the code to identify a list of customer IDs for this advertising campaign.