text: DROP TABLE referral;
  DROP TYPE REFERRAL_STATUS;
  
  ALTER TABLE request DROP COLUMN own_referral_code,
                      DROP COLUMN registration_referral_code;
  DROP TRIGGER trigger_request_unique_referral_code ON request;
  DROP FUNCTION IF EXISTS unique_referral_code();
  DROP FUNCTION IF EXISTS referral_tracking_sender_stats(addr VARCHAR, since INTERVAL);