CREATE TABLE event (ID NUMBER, Name CLOB, Stadium_ID NUMBER, Year CLOB)
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 record (ID NUMBER, Result CLOB, Swimmer_ID NUMBER, Event_ID NUMBER)
CREATE TABLE stadium (ID NUMBER, name CLOB, Capacity NUMBER, City CLOB, Country CLOB, Opening_year NUMBER)

Bar chart x axis nationality y axis how many nationality, and list in descending by the Y-axis.
SELECT Nationality, COUNT(Nationality) FROM swimmer GROUP BY Nationality ORDER BY COUNT(Nationality) DESC
SELECT "Nationality", COUNT("Nationality") FROM "swimmer" GROUP BY "Nationality" ORDER BY COUNT("Nationality") DESC