Which courses have at least five enrollments?
SELECT * FROM COURSE AS T1 JOIN ENROLLED_IN AS T2 ON T1.CID   =   T2.CID GROUP BY T2.CID HAVING COUNT ( * )    > =    5
courses with at least five enrollments refers to HAVING COUNT(*) >= 5; joining courses with enrollments refers to JOIN ENROLLED_IN ON COURSE.CID = ENROLLED_IN.CID;