three.sql

SELECT cno, dname, b.count_of_students
FROM
	(SELECT COUNT(*) AS num_of_students
	FROM student s, enroll e
	WHERE s.sid = e.sid) a,
	(
	SELECT c.cno, c.dname, COUNT(*) as count_of_students
	FROM course c RIGHT OUTER JOIN enroll e
	ON c.cno = e.cno
	WHERE c.cno = e.cno AND c.dname = e.dname
	GROUP BY c.cno, c.dname) b

WHERE b.count_of_students < 0.08 * a.num_of_students