/*Write a SQL statement to make a cartesian product between salesman and customer i.e. each salesman will appear for all 
customer and vice versa for those salesmen who must belong a city which is not the same as his customer and the customers 
should have an own grade.*/
SELECT *   
FROM salesman a   
CROSS JOIN customer b   
WHERE a.city IS NOT NULL   
AND b.grade IS NOT NULL   
AND  a.city<>b.city;