Which cities have more than one airport?
select city from airports group by city having count ( * ) > 1
Now show the number of airports in each of those cities
select city, count ( * ) from airports group by city having count ( * ) > 1
Which cities have three airports
select city from airports group by city having count ( * ) = 3
Which cities have 4 or more airports
select city from airports group by city having count ( * ) > = 4
Show the number of airports in those cities
select city, count ( * ) from airports group by city having count ( * ) > = 4