How old is Dan?
select age from person where name = 'Dan'
What city is she from?
select city from person where name = 'Dan'
Show all friends of Dan.
select * from personfriend where name = 'Dan'
How many friends is this?
select count(t2.friend) from person as t1 join personfriend as t2 on t1.name = t2.name where t1.name = 'Dan'