GTFS SQL Find Closest Routes - mysql

Question

I have a MySQL database setup with GTFS data and I am trying to query the database to return a list of routes (no duplicates) ordered by the distance to the closest stop on each respective route. (Note: The coordinates will change depending on where the user is)
The database is rather large (millions of rows in the stop_times table, 10,000s of rows in the stops table) so I want to make this as efficient as possible.
One thing I tried was to create a temporary table called stop_routes_link (created when the GTFS data is imported into my database) that links stops with routes such that there is an entry for each stop-route pair like so:
route_id | stop_id
-----------------------
25 | 366072709
21 | 366072709
21 | 194326291
F | 60745282
Q | 198000482
And then I ran this query which works perfectly:
SELECT routes.route_short_name AS route_short_name
FROM routes
LEFT JOIN (
SELECT ( 3959 * acos( cos( radians(39.94868155755109) ) * cos( radians( stops.stop_lat ) ) * cos( radians( stops.stop_lon ) - radians(-75.15972534860013) ) + sin( radians(39.94868155755109) ) * sin( radians( stops.stop_lat ) ) ) ) AS distance, stop_routes_link.route_id AS route_id
FROM stops
LEFT JOIN stop_routes_link ON stops.stop_id = stop_routes_link.stop_id ORDER BY distance)
AS stops ON routes.route_id = stops.route_id
ORDER BY stops.distance
And it returns:
route_short_name
----------------
23
23
12
12
9
21
38
Which is what I want (I know those are the closest routes to that location), except it returns duplicates for routes since I think it is returning an row for each stop on a route.
How do I return only unique routes? I thought that the "LEFT JOIN" would cause only one row per entry in the routes table but it didn't.
I've also tried:
SELECT DINSTINCT routes.route_short_name AS route_short_name
FROM routes
LEFT JOIN (
SELECT ( 3959 * acos( cos( radians(39.94868155755109) ) * cos( radians( stops.stop_lat ) ) * cos( radians( stops.stop_lon ) - radians(-75.15972534860013) ) + sin( radians(39.94868155755109) ) * sin( radians( stops.stop_lat ) ) ) ) AS distance, stop_routes_link.route_id AS route_id
FROM stops
LEFT JOIN stop_routes_link ON stops.stop_id = stop_routes_link.stop_id ORDER BY distance)
AS stops ON routes.route_id = stops.route_id
ORDER BY stops.distance
And:
SELECT routes.route_short_name AS route_short_name
FROM routes
LEFT JOIN (
SELECT ( 3959 * acos( cos( radians(39.94868155755109) ) * cos( radians( stops.stop_lat ) ) * cos( radians( stops.stop_lon ) - radians(-75.15972534860013) ) + sin( radians(39.94868155755109) ) * sin( radians( stops.stop_lat ) ) ) ) AS distance, stop_routes_link.route_id AS route_id
FROM stops
LEFT JOIN stop_routes_link ON stops.stop_id = stop_routes_link.stop_id ORDER BY distance)
AS stops ON routes.route_id = stops.route_id
GROUP BY route_short_name
ORDER BY stops.distance
But they both don't return the closest routes they return a random ordered list of routes (I'm not sure how it is calculated) which I'm assuming is because the grouping messes it up.
Any help would be greatly appreciated!