How many events are there?
select count(*) from event
What about in terms of stadiums?
select stadium_id,count(*) from event group by stadium_id
Give me the name of the one that held the most of them.
select t1.name from stadium as t1 join event as t2 on t1.id = t2.stadium_id group by t2.stadium_id order by count(*) desc limit 1