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"