text: delimiter $$
  create trigger for_railway_zones before insert on railway_zones
  for each row
  begin
   if new.zone_id = '' then
   signal sqlstate '45000';
   end if;
  end;$$
  delimiter ;
  
  
  INSERT IGNORE INTO railway_zones (zone_id,zone_name) VALUES (1,"south");
  INSERT IGNORE INTO railway_zones (zone_id,zone_name) VALUES (2,"north");
  INSERT IGNORE INTO railway_zones (zone_id,zone_name) VALUES (3,"west");
  INSERT IGNORE INTO railway_zones (zone_id,zone_name) VALUES (4,"east");