What is the ratio of professors and students?
professors refers to professor = 1; students refers to student = 1; ratio = divide(count(person.p_id) when professor = 1, count(person.p_id) when student = 1)
SELECT CAST(SUM(CASE  WHEN professor = 1 THEN 1 ELSE 0 END) AS REAL) * 100 / SUM(CASE  WHEN student = 1 THEN 1 ELSE 0 END) AS per FROM person