CREATE TABLE customers (customer_name VARCHAR, customer_id VARCHAR)
CREATE TABLE customer_orders (customer_id VARCHAR)

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"