ค้นหาชื่ออาจารย์ที่กำลังสอนสองหลักสูตร รหัส CIS-220 และ QM-261 ไม่จำเป็นต้องใช้ทุกตาราง
Find the first name of the professor who is teaching two courses with code CIS-220 and QM-261.It is not neccessary to use all the tables.
 professor:  emp_num [ number]  dept_code [ text]  prof_office [ text]  prof_extension [ text]  prof_high_degree [ text] 
SELECT T1.emp_fname FROM employee AS T1 JOIN class AS T2 ON T1.emp_num = T2.prof_num WHERE crs_code = 'CIS-220' INTERSECT SELECT T1.emp_fname FROM employee AS T1 JOIN class AS T2 ON T1.emp_num = T2.prof_num WHERE crs_code = 'QM-261'