List all the country names.
select country_name from country
For all players, show their country names.
select t2.player, country_name from country as t1 join match_season as t2 on t1.country_id = t2.country group by t1.country_name
For each country, how many players are there?
select country_name, count(*) from country as t1 join match_season as t2 on t1.country_id = t2.country group by t1.country_name