How many students are advised to teach by a professor teaching basic or medium undergraduate courses?
students refers to advisedBy.p_id; professor refers to p_id_dummy and taughtBy.p_id and professor = 1; basic or medium undergraduate courses refers to courseLevel = 'Level_300'
SELECT COUNT(DISTINCT T4.p_id) FROM person AS T1 INNER JOIN taughtBy AS T2 ON T1.p_id = T2.p_id INNER JOIN course AS T3 ON T3.course_id = T2.course_id INNER JOIN advisedBy AS T4 ON T4.p_id = T1.p_id WHERE T1.professor = 1 AND T3.courseLevel = 'Level_300'