ALTER TABLE jam_tracks DROP COLUMN preview_url;
ALTER TABLE jam_tracks DROP COLUMN preview_md5;
ALTER TABLE jam_tracks DROP COLUMN preview_length;
ALTER TABLE jam_tracks DROP COLUMN preview_start_time;

ALTER TABLE jam_track_tracks ADD COLUMN preview_url VARCHAR;
ALTER TABLE jam_track_tracks ADD COLUMN preview_md5 VARCHAR;
ALTER TABLE jam_track_tracks ADD COLUMN preview_length BIGINT;
ALTER TABLE jam_track_tracks ADD COLUMN preview_start_time INTEGER;