Make sure date of departure is different than date of arrival?

Question

I have the following tables:

• Flights (id_flight)

• Airports (id_airport)

• Departures_Arrivals (id_flight, id_airport), which is the Junction Table between Flights and Airports and it has the following attributes:

  • gate

  • date

  • type, which can be either 0 or 1, where 0 stands for departure and 1 stands for arrival.

Is there any kind of constraint to make sure that the date of the arrival is greater than the date of the departure?

Answer 1

Make a BEFORE INSERT TRIGGER, which checks in case of an Inserting a row for that flight and Airport the condition is met.

This is an example, you have ti check the conditions and error message if the condition is not met.

DELIMITER $$

CREATE TRIGGER before_Departures_Arrivals_insert
BEFORE INSERT
ON Departures_Arrivals FOR EACH ROW
BEGIN
    DECLARE _date  DATETIME;
    DECLARE _tyoe  INTEGER;

    IF NEW.tyoe = 1 THEN
        SET _type = 0;
    ELSE
        SET _type = 1;
    END IF;

    SELECT `date`
    INTO _date
    FROM Departures_Arrivals 
    WHERE id_flight = NEW.id_flight AND  id_airport = NEW.id_airport
            AND type = _type
    ORDER BY `date` DESC
    LIMIT 1;

    IF NEW.`date` > _date THEN
        SIGNAL SQLSTATE '45000' 
        SET MESSAGE_TEXT = "The new date is before the arrival";
    END IF; 

END $$

DELIMITER ;