Find all employees who taught a course?
select * from class as t1 join employee as t2 on t1.prof_num = t2.emp_num
What are their first names?
select t2.emp_fname from class as t1 join employee as t2 on t1.prof_num = t2.emp_num
Also, what are the course descriptions of their classes?
select t2.emp_fname, t3.crs_description from class as t1 join employee as t2 on t1.prof_num = t2.emp_num join course as t3 on t1.crs_code = t3.crs_code