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 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)

A pie chart for finding the number of the names of stadiums that some Australian swimmers have been to.
SELECT T4.Name, COUNT(T4.Name) FROM swimmer AS t1 JOIN record AS t2 ON t1.ID = t2.Swimmer_ID JOIN event AS t3 ON t2.Event_ID = t3.ID JOIN stadium AS t4 ON t4.ID = t3.Stadium_ID WHERE t1.Nationality = 'Australia' GROUP BY T4.Name
SELECT "T4"."Name", COUNT("T4"."Name") FROM "swimmer" "t1" JOIN "record" "t2" ON "t1"."ID" = "t2"."Swimmer_ID" JOIN "event" "t3" ON "t2"."Event_ID" = "t3"."ID" JOIN "stadium" "t4" ON "t3"."Stadium_ID" = "t4"."ID" WHERE "t1"."Nationality" = 'Australia' GROUP BY "T4"."Name"