CREATE TABLE swimmer (ID NUMBER, name CLOB, Nationality CLOB, meter_100 FLOAT, meter_200 CLOB, meter_300 CLOB, meter_400 CLOB, meter_500 CLOB, meter_600 CLOB, meter_700 CLOB, Time CLOB)
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 event (ID NUMBER, Name CLOB, Stadium_ID NUMBER, Year CLOB)

Show the average of id from each nationality, display mean id in desc order.
SELECT Nationality, AVG(ID) FROM swimmer GROUP BY Nationality ORDER BY AVG(ID) DESC
SELECT "Nationality", AVG("ID") FROM "swimmer" GROUP BY "Nationality" ORDER BY AVG("ID") DESC