ค้นหารหัสของผู้ใช้ที่ตามมาด้วย Mary และ Susan ไม่จำเป็นต้องใช้ตารางทั้งหมด
Find the id of users who are followed by Mary and Susan.It is not neccessary to use all the tables.
 follows:  (f1 [ VARCHAR ] f2 [ VARCHAR) ]
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"