text: ALTER TABLE `order` DROP FOREIGN KEY order_ibfk_4;
  ALTER TABLE `order` DROP FOREIGN KEY order_ibfk_5;
  
  ALTER TABLE `order` ADD CONSTRAINT `order_ibfk4` FOREIGN KEY(`id_session`) REFERENCES `session`(`id_session`) ON DELETE CASCADE ON UPDATE SET NULL;
  ALTER TABLE `order` ADD CONSTRAINT `order_ibfk5` FOREIGN KEY(`id_agent`) REFERENCES `agent`(`id_agent`) ON DELETE CASCADE ON UPDATE SET NULL;