-- Database schema
| race : Race_ID [ INT ] primary_key , Name [ TEXT ] , Class [ TEXT ] , Date [ TEXT ] , Track_ID [ TEXT ] race.Track_ID = track.Track_ID | track : Track_ID [ INT ] primary_key , Name [ TEXT ] , Location [ TEXT ] , Seating [ INT ] , Year_Opened [ INT ] |
-- -- List the race class with at least two races.

SELECT CLASS FROM race GROUP BY CLASS HAVING count(*)  >=  2;