Show names for all aircraft.
select name from aircraft
For each of them, also show the number of flights.
select t2.name, count(*) from flight as t1 join aircraft as t2 on t1.aid = t2.aid group by t1.aid
Which two have the fewest?
select t2.name from flight as t1 join aircraft as t2 on t1.aid = t2.aid group by t1.aid having count(*) >= 2