Question

I have just started learning MySQL and am having trouble extracting matching flights from my database (I have spent days trying different solutions to no avail!). My database holds fictitious flight data where outbound and return flights are multiples of 1 week apart.

I am looking to design a query which checks for the existence of and then fetches pairs of outgoing and return flights for +/- 3 days of the departure date selected by the user. I need the flights to be ordered by outbound flight and then the matching return flight as I will be outputting the results with PHP’s mysql_fetch_array while loop.

So far I have been experimenting with IF (EXISTS(SELECT conditions within the WHERE clause to check whether the outbound flight exists, and if it is true (does exist) then return the outbound and return flight. This works ok for when testing for one date but I’m not sure how to integrate it into a date range unless I can use a while loop in mysql? I have also read it is not ideal to have IF statements within the WHERE clause as it increases the query time.

The return date is calculated in PHP by adding the ‘duration’ option in the user form (i.e. 1 week, 2 weeks etc) to the out date.

I have copied the query code I have so far below but I appreciate there may be a lot simpler/better way of achieving my desired result and would be grateful for any guidance. My code will return a matching pair of flights only for the specific date supplied to it as I’m not sure how to implement a +/- 3 day search AND keep the results in the order of outbound and return flight pairs.

Thanks,
Gary

SELECT 
sched.flight_schedule_id, dep_airport, dest_airport, code, dep_time, arr_time, flight_time, dep_date, dep.airport_name, dep.airport_country, adult_flight_price, dest.airport_name, dest.airport_country, plane.no_seats, sum(adult_seats_reserved), sum(child_seats_reserved)

        FROM 
            flight fli

            INNER JOIN flight_schedule sched
            ON fli.flight_id = sched.flight_id

            INNER JOIN airport dep
            ON fli.dep_airport = dep.airport_code

            INNER JOIN airport dest
            ON fli.dest_airport = dest.airport_code

            INNER JOIN plane_type plane
            ON fli.plane_id = plane.plane_id

            LEFT JOIN flight_inventory inv
            ON sched.flight_schedule_id = inv.flight_schedule_id    

        WHERE 

        IF (EXISTS(SELECT
            sched.flight_schedule_id, dep_airport, dest_airport, code, dep_time, arr_time, flight_time, dep_date, dep.airport_name, dep.airport_country, adult_flight_price, dest.airport_name, dest.airport_country

            FROM 
                flight fli

                INNER JOIN flight_schedule sched
                ON fli.flight_id = sched.flight_id

                INNER JOIN airport dep
                ON fli.dep_airport = dep.airport_code

                INNER JOIN airport dest
                ON fli.dest_airport = dest.airport_code

                LEFT JOIN flight_inventory inv
                ON sched.flight_schedule_id = inv.flight_schedule_id

            WHERE 


            dep.airport_name = '$to' AND dest.airport_name = '$from' AND sched.dep_date = '$return'),

            (dep.airport_name = '$from' AND dest.airport_name = '$to' AND sched.dep_date = '$outdate')

        OR

            (dep.airport_name = '$to' AND dest.airport_name = '$from' AND sched.dep_date = '$return'), '')

        GROUP BY

            sched.flight_schedule_id

Answer 1

This might help you. It’s a fresh solution that should solve your problem. I did not include the numerous JOINs from your query, but adding them is trivial. To make the +/- 3 days part work, I assumed your dep_date to be of type TIMESTAMP and your $outdate and $return to be unix timestamps as well. ABS is just the absolute value, i.e. ABS(-x) = ABS(x) = x

SELECT
    * 
FROM 
    flight_schedule outbound
JOIN
    flight_schedule return 
    ON
        /* return flights should depart from outbounds destination */
        outbound.dest_airport = return.dep_airport
    AND
        /* optional. might reduce intermediate join result size */
        outbound.arr_date < return.dep_date 

WHERE
    /* user wants to fly from airport $from to airport $to */
    outbound.dep_airport = '$from'
    AND outbound.dest_airport = '$to'

    /* outbound flight should depart within 3 days before and after $outdate (3 days = 259200 seconds) */
    AND ABS(outbound.dep_date - $outdate) < 259200

    /* return flight should depart within 3 days before and after $return */
    AND ABS(return.dep_date - $return) < 259200

ORDER BY
    /* order outbound flights by distance to user's requested $outdate */
    ABS(outbound.dep_date - $outdate) ASC,

    /* and return flights by distance to user's requested $return date */
    ABS(return.dep_date - $return) ASC

If you have the type DATE for the column dep_date you can still use BETWEEN like

WHERE outbound.dep_date BETWEEN
        DATE_SUB($outdate, INTERVAL 3 DAY)
    AND DATE_ADD($outdate, INTERVAL 3 DAY)

using MySQL’s DATE_ADD and DATE_SUB functions or DATEDIFF

WHERE
    ABS(DATEDIFF(outbound.dep_date, $outdate)) < 259200

and sort using DATEDIFF as well

ORDER BY 
    ABS(DATEDIFF(outbound.dep_date, $outdate)) ASC,
    ABS(DATEDIFF(return.dep_date, $return)) ASC