can you please tell me if Alice is friends with Bob?
select t1.name from person as t1 join personfriend as t2 on t1.name = t2.name where t2.friend = 'Bob'
great. and who are Zach's friends?
select * from person as t1 join personfriend as t2 on t1.name = t2.name where t2.friend = 'Zach'
and can you tell me, besides Alice and Zach, is there anyone else who is friends with Bob?
select t1.name from person as t1 join personfriend as t2 on t1.name = t2.name where t2.friend = 'Bob' and t1.name ! = "Alice" and t1.name ! = "Zach"