Which countries do players come from?
select birth_country from player
How many players are from each country?
select birth_country, count(*) from player group by birth_country
Which country provided the most players?
select birth_country from player group by birth_country order by count(*) desc limit 1;
What are the three countries that provided the fewest players?
select birth_country from player group by birth_country order by count(*) asc limit 3;