/* list suppliers who have QTYs greater than the the QTYs of s4 */
select snumber, qty
from spj
where qty > ALL
(select qty
from spj
where snumber = 's4');


/*List suppliers who have qty smaller than any qty of s2*/

SELECT snumber, qty
FROM spj
WHERE qty < ANY(SELECT qty FROM spj WHERE snumber = "s2");

/*List the snumber and QTYs of the supplier who relates with the snumber to the QTYs that are greater than the AVG QTYs of the particular supplier.
i.e. for s1 the AVG of all its QTY is x... You must list all the QTYs of s1 that are greater than x.
*/
select snumber, qty
from spj as a 
where qty > 
(select avg(qty)
 from spj
 where a.snumber = snumber);
 
 
 /* EXISTS demo */
 
 select *
from supplier a
where not EXISTS
	(select * from spj
    where snumber = a.snumber);