CREATE TABLE employee (EMP_NUM VARCHAR2, EMP_LNAME VARCHAR2)
CREATE TABLE CLASS (PROF_NUM VARCHAR2)

How many classes are professor whose last name is Graztevski has?
SELECT COUNT(*) FROM employee AS T1 JOIN CLASS AS T2 ON T1.EMP_NUM = T2.PROF_NUM WHERE T1.EMP_LNAME = 'Graztevski'
SELECT COUNT(*) FROM "employee" "T1" JOIN "CLASS" "T2" ON "T1"."EMP_NUM" = "T2"."PROF_NUM" WHERE "T1"."EMP_LNAME" = 'Graztevski'