Table schema:
CREATE TABLE employee (emp_fname VARCHAR, emp_jobcode VARCHAR); CREATE TABLE CLASS (prof_num VARCHAR); CREATE TABLE employee (emp_fname VARCHAR, emp_num VARCHAR)

Question: What are the first names of the professors who do not teach a class.
SQL: SELECT emp_fname FROM employee WHERE emp_jobcode = 'PROF' EXCEPT SELECT T1.emp_fname FROM employee AS T1 JOIN CLASS AS T2 ON T1.emp_num = T2.prof_num