Which employees have taught some course?
select * from class as t1 join employee as t2 on t1.prof_num = t2.emp_num
What are these courses' descriptions?
select 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
Also, what are their office locations and the professors' first names?
select t2.emp_fname, t4.prof_office, 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 join professor as t4 on t2.emp_num = t4.emp_num