Question: Find the id of users who are followed by Mary and Susan.
SQL: SELECT T2.f1 FROM user_profiles AS T1 JOIN follows AS T2 ON T1.uid  =  T2.f2 WHERE T1.name  =  "Mary" INTERSECT SELECT T2.f1 FROM user_profiles AS T1 JOIN follows AS T2 ON T1.uid  =  T2.f2 WHERE T1.name  =  "Susan"