What are the first names of all employees?
select emp_fname from employee
who are teaching some courses?
select t2.emp_fname from class as t1 join employee as t2 on t1.prof_num = t2.emp_num
Also, what courses do they teach?
select t2.emp_fname, t1.crs_code from class as t1 join employee as t2 on t1.prof_num = t2.emp_num