Tell me about all the airports.
select * from airport
Tell me the names of these airports.
select name from airport
How many companies operate in "Akureyi airport"?
select count(t2.company_id) from airport as t1 join flight as t2 on t1.id = t2.airport_id group by t1.id having t1.name = "Akureyri Airport"
What about for each airport?
select t3.id, count(*) from operate_company as t1 join flight as t2 on t1.id = t2.company_id join airport as t3 on t2.airport_id = t3.id group by t3.id