แต่ละโรงเรียนมีจำนวนอาจารย์กี่คน?ไม่จำเป็นต้องใช้ตารางทั้งหมด
What is the number of professors for different school?It is not neccessary to use all the tables.
 department:  (school_code [ VARCHAR ] dept_code [ VARCHAR) ]
SELECT COUNT(*), T1.school_code FROM department AS T1 JOIN professor AS T2 ON T1.dept_code = T2.dept_code GROUP BY T1.school_code