Can you show me the name of the customer who purchased the least quantity of items?
SELECT t1.customer_name FROM customers AS t1 JOIN customer_orders AS t2 ON t1.customer_id   =   t2.customer_id JOIN order_items AS t3 ON t2.order_id   =   t3.order_id GROUP BY t1.customer_name ORDER BY sum ( t3.order_quantity )  LIMIT 1
least quantity of items refers to MIN(SUM(order_quantity)); name of the customer refers to customer_name;