INTERSECTION OPERATOR
Find the salespeople who have taken orders of more than 1000 and who have less than 2 customers assigned.
SELECT snum FROM Orders a
WHERE 1000 < (SELECT SUM(amount) FROM Orders b WHERE b.snum = a.snum)
INTERSECT
SELECT snum FROM Salespeople c WHERE 2 > (SELECT count(*) FROM Customers d WHERE d.snum = c.snum);