GTFS MySQL Query Column Not Found - php

Question

Im working with GTFS dataset that I have imported into MySql, Im accessing it with PHP.
Im trying to find the trips for a specific route for a given time and date.
My Sql query looks like this
'SELECT t.route_id AS route_id, t.service_id AS service_id, t.trip_headsign AS trip_headsign,
t.trip_id AS trip_id,
( SELECT departure_time
FROM stop_times
WHERE trip_id = t.trip_id
ORDER BY departure_time ASC limit 1) AS initial_departure_time,
( SELECT arrival_time
FROM stop_times
WHERE trip_id = t.trip_id
ORDER BY arrival_time DESC limit 1) AS final_arrival_time
FROM trips AS t INNER JOIN calendar_dates AS c
WHERE t.service_id = c.service_id
AND c.date ='.$calendar_date.'
AND initial_departure_time <='.$time.'
AND'.$time. '<=final_arrival_time
AND t.route_id ='.$route.'
ORDER BY trip_id ASC';
$route, $calendar_date and $time are all passed in.
The query is returning Column not found:
1054 Unknown column 'initial_departure_time' in 'where clause'. Im thinking that initial_departure_time cant be evaluated.
Im completely lost as too how to resolve this. Any clues, thanks in advance

Answer 1

You can't use aliases in your WHERE clause.
Either incorporate the sub-queries into the WHERE clause:
'SELECT t.route_id AS route_id,
t.service_id AS service_id,
t.trip_headsign AS trip_headsign,
t.trip_id AS trip_id,
(SELECT departure_time
FROM stop_times
WHERE trip_id = t.trip_id
ORDER BY departure_time ASC limit 1) AS initial_departure_time,
(SELECT arrival_time
FROM stop_times
WHERE trip_id = t.trip_id
ORDER BY arrival_time DESC limit 1) AS final_arrival_time
FROM trips AS t INNER JOIN calendar_dates AS c
WHERE t.service_id = c.service_id
AND c.date ='.$calendar_date.'
AND (SELECT departure_time
FROM stop_times
WHERE trip_id = t.trip_id
ORDER BY departure_time ASC limit 1) <='.$time.'
AND'.$time. '<= (SELECT arrival_time
FROM stop_times
WHERE trip_id = t.trip_id
ORDER BY arrival_time DESC limit 1)
AND t.route_id ='.$route.'
ORDER BY trip_id ASC';
Or wrap the query and then use the aliases in that:
'SELECT * FROM (
SELECT t.route_id AS route_id,
t.service_id AS service_id,
t.trip_headsign AS trip_headsign,
t.trip_id AS trip_id,
(SELECT departure_time
FROM stop_times
WHERE trip_id = t.trip_id
ORDER BY departure_time ASC limit 1) AS initial_departure_time,
(SELECT arrival_time
FROM stop_times
WHERE trip_id = t.trip_id
ORDER BY arrival_time DESC limit 1) AS final_arrival_time
FROM trips AS t INNER JOIN calendar_dates AS c
WHERE t.service_id = c.service_id
AND c.date ='.$calendar_date.'
AND t.route_id ='.$route.'
ORDER BY trip_id ASC) a
WHERE a.initial_departure_time <='.$time.'
AND'.$time. '<= a.final_arrival_time';
This might speed it up (you may need to swap the MIN and MAX around):
'SELECT t.route_id AS route_id,
t.service_id AS service_id,
t.trip_headsign AS trip_headsign,
t.trip_id AS trip_id,
MIN(s.departure_time) AS initial_departure_time,
MAX(s.arrival_time) AS final_arrival_time
FROM trips AS t
INNER JOIN calendar_dates AS c ON t.service_id = c.service_id
LEFT JOIN stop_times s ON s.trip_id = t.trip_id
WHERE c.date ='.$calendar_date.'
AND t.route_id ='.$route.'
GROUP BY t.route_id, t.service_id, t.trip_headsign, t.trip_id,
HAVING '.$time.' BETWEEN MAX(s.arrival_time) AND MIN(s.departure_time)
ORDER BY trip_id ASC';