ค้นหาเพื่อนของอลิซ ไม่จำเป็นต้องใช้ตารางทั้งหมด
Find Alice's friends of friends.It is not neccessary to use all the tables.
 PersonFriend:  (name [ VARCHAR) ]
SELECT DISTINCT T4.name FROM PersonFriend AS T1 JOIN Person AS T2 ON T1.name = T2.name JOIN PersonFriend AS T3 ON T1.friend = T3.name JOIN PersonFriend AS T4 ON T3.friend = T4.name WHERE T2.name = 'Alice' AND T4.name <> 'Alice'