Table schema:
CREATE TABLE professor (emp_num VARCHAR, dept_code VARCHAR); CREATE TABLE department (dept_code VARCHAR, dept_name VARCHAR); CREATE TABLE CLASS (prof_num VARCHAR); CREATE TABLE employee (emp_fname VARCHAR, emp_num VARCHAR)

Question: What is the first names of the professors from the history department who do not teach a class.
SQL: SELECT T1.emp_fname FROM employee AS T1 JOIN professor AS T2 ON T1.emp_num = T2.emp_num JOIN department AS T3 ON T2.dept_code = T3.dept_code WHERE T3.dept_name = 'History' EXCEPT SELECT T4.emp_fname FROM employee AS T4 JOIN CLASS AS T5 ON T4.emp_num = T5.prof_num