CREATE TABLE swimmer (id DECIMAL, name TEXT, nationality TEXT, meter_100 DECIMAL, meter_200 TEXT, meter_300 TEXT, meter_400 TEXT, meter_500 TEXT, meter_600 TEXT, meter_700 TEXT, time TEXT)
CREATE TABLE record (id DECIMAL, result TEXT, swimmer_id DECIMAL, event_id DECIMAL)
CREATE TABLE event (id DECIMAL, name TEXT, stadium_id DECIMAL, year TEXT)
CREATE TABLE stadium (id DECIMAL, name TEXT, capacity DECIMAL, city TEXT, country TEXT, opening_year DECIMAL)

Find the country that has the most stadiums.
SELECT country FROM stadium GROUP BY country ORDER BY COUNT(*) DESC LIMIT 1
SELECT "country" FROM "stadium" GROUP BY "country" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1