ALTER TABLE `travel_changelog` 
ADD COLUMN `immediateexit` ENUM('YES', 'NO') NULL AFTER `change_date`;

ALTER TABLE `travel_changelog` 
DROP FOREIGN KEY `fk_travel_changelog_travel2`;
ALTER TABLE `travel_changelog` 
CHANGE COLUMN `serial_trv_to` `serial_trv_to` INT(11) NULL ;
ALTER TABLE `travel_changelog` 
ADD CONSTRAINT `fk_travel_changelog_travel2`
  FOREIGN KEY (`serial_trv_to`)
  REFERENCES `travel` (`serial_trv`)
  ON DELETE NO ACTION
  ON UPDATE NO ACTION;