SELECT Class, COUNT(Class) FROM race GROUP BY Class
Show me the proportion of classes of all races using a pie chart.
CREATE TABLE track (
    Track_ID int,
    Name text,
    Location text,
    Seating real,
    Year_Opened real
)

CREATE TABLE race (
    Race_ID int,
    Name text,
    Class text,
    Date text,
    Track_ID text
)