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

Which country has both stadiums with capacity greater than 60000 and stadiums with capacity less than 50000?
SELECT country FROM stadium WHERE capacity > 60000 INTERSECT SELECT country FROM stadium WHERE capacity < 50000
SELECT "country" FROM "stadium" WHERE "capacity" > 60000 INTERSECT SELECT "country" FROM "stadium" WHERE "capacity" < 50000