What is the total number of products that are in orders with status "Delivered"?
SELECT sum ( t2.order_quantity )  FROM customer_orders AS t1 JOIN order_items AS t2 ON t1.order_id   =   t2.order_id WHERE t1.order_status   =   "Delivered"
total number refers to SUM(order_quantity); orders with status 'Delivered' refers to WHERE order_status = 'Delivered';