ALTER TABLE merchandise_distribution
  ADD COLUMN schedule_id BIGINT NULL AFTER ticket_id,
  ADD COLUMN checkin_log_id BIGINT NULL AFTER schedule_id,
  ADD INDEX idx_merch_distribution_schedule (schedule_id),
  ADD INDEX idx_merch_distribution_checkin (checkin_log_id),
  ADD CONSTRAINT fk_merchdist_schedule FOREIGN KEY (schedule_id) REFERENCES event_schedules(id) ON DELETE SET NULL,
  ADD CONSTRAINT fk_merchdist_checkin FOREIGN KEY (checkin_log_id) REFERENCES event_checkin_logs(id) ON DELETE SET NULL;