Getting the item with the most sales

Question

I have an Order table which has an order_id, item_id, product_id, quantity, price, total. Now what i'm concerned about is the total and the product_id because i want to find out which item has the highest sales. Which sum(total) is the highest. But I also have to link this up to a customer, the customer_id is in another table which joins to the order table through the order_id. How could i find out which product each customer has ordered the most.

Answer 1

Not the most elegant, but...
SELECT * FROM
  (SELECT X.NAME, TO_CHAR(X.TOTAL,'$999,999.99') TOTAL, X.DESCRIPTION,  ROUND( ((TOTAL / ALL_TOTAL)*100) ,2)
     FROM(select A.CUSTOMER_ID,a.name, SUM(b.quantity*b.actual_price) TOTAL, c.description
             from customer a, item b, product c, sales_order d
             where A.CUSTOMER_ID = D.CUSTOMER_ID
               AND D.ORDER_ID = B.ORDER_ID
               AND B.PRODUCT_ID = C.PRODUCT_ID
             GROUP BY A.CUSTOMER_ID, A.NAME, C.DESCRIPTION) X,
           (SELECT A.CUSTOMER_ID,A.NAME, SUM(b.quantity*b.actual_price) ALL_TOTAL
               from customer a, item b, product c, sales_order d
               where A.CUSTOMER_ID = D.CUSTOMER_ID
                 AND D.ORDER_ID = B.ORDER_ID
                 AND B.PRODUCT_ID = C.PRODUCT_ID
             GROUP BY A.CUSTOMER_ID, A.NAME) Y
     WHERE X.CUSTOMER_ID = Y.CUSTOMER_ID
  ORDER BY X.TOTAL DESC)
WHERE ROWNUM=1