/*Write a SQL statement that shorts out the customer and their grade who made an order. Each of the customers 
must have a grade and served by at least a salesman, who belongs to a city.*/
SELECT customer.cust_name AS "Customer",  
customer.grade AS "Grade"  
FROM orders, salesman, customer  
WHERE orders.customer_id = customer.customer_id  
AND orders.salesman_id = salesman.salesman_id  
AND salesman.city IS NOT NULL  
AND customer.grade IS NOT NULL;