What are the first names, office locations of all lecturers who have taught some course?
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
first names refers to emp_fname; office locations refers to prof_office; all lecturers who have taught some course involves joining tables: CLASS, employee, course, and professor on respective keys (prof_num, emp_num, crs_code);