CREATE TABLE race (race_id DECIMAL, name TEXT, class TEXT, date TEXT, track_id TEXT)
CREATE TABLE track (track_id DECIMAL, name TEXT, location TEXT, seating DECIMAL, year_opened DECIMAL)

What is the race class with most number of races.
SELECT class FROM race GROUP BY class ORDER BY COUNT(*) DESC LIMIT 1
SELECT "class" FROM "race" GROUP BY "class" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1