Show all cities alphabetically.
select city from person order by city
How many people live in Austin?
select count(*) from person where city = 'austin'
Who is friends with them?
select name from personfriend where friend in (select name from person where city = 'austin')
How many people are not friends with them?
select count(distinct name) from personfriend where friend not in (select name from person where city = 'Austin')