Table schema:
CREATE TABLE CLASS (PROF_NUM VARCHAR); CREATE TABLE employee (EMP_NUM VARCHAR, EMP_LNAME VARCHAR)

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