How many stadiums are there?
select count(*) from stadium
How many Australian swimmers are there in the record?
select count(*) from swimmer where nationality = 'Australian'
Show me the stadiums any of those swimmers have been to.
select t4.name from swimmer as t1 join record as t2 on t1.id = t2.swimmer_id join event as t3 on t2.event_id = t3.id join stadium as t4 on t4.id = t3.stadium_id where t1.nationality = 'Australia'