Can you list the names of all the customers who never placed a single 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
What date did they each become customers?
select date_became_customer from customers where customer_name in ( 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 )
What are the names of the customers who cancelled their orders?
select distinct t1.customer_name from customers as t1 join customer_orders as t2 on t1.customer_id = t2.customer_id where t2.order_status = "Cancelled"