Find the names of customers who never placed an order.
SELECT customer_name FROM customers EXCEPT SELECT t1.customer_name FROM customers AS t1 JOIN customer_orders AS t2 ON t1.customer_id  =  t2.customer_id
SELECT customer_name FROM customers EXCEPT SELECT t1.customer_name FROM customers AS t1 JOIN customer_orders AS t2 ON t1.customer_id  =  t2.customer_id
[{'customer_name': 'Alexane Kilback'}, {'customer_name': 'Devin Mills'}, {'customer_name': 'Dr. Julia Wuckert MD'}, {'customer_name': 'Maudie Kertzmann'}, {'customer_name': 'Miss Aliyah Witting'}, {'customer_name': 'Mozell Morissette'}, {'customer_name': 'Tillman Ernser'}]