Finding the routes associated with a stop in GTFS, not vice versa (maybe similar)

I hope someone can help.

Hi am building a transit app for Android and I have hit a snag.

I would like to get all of the busses/routes which service a particular stop.

e.g. Stop No: 12345 have Busses: 123 & 321.

I have this piece of SQL:

SELECT DISTINCT rt.route_short_name
FROM routes rt
LEFT JOIN trips tr
ON rt.route_id = tr.route_id
LEFT JOIN stop_times st
ON tr.trip_id = st.trip_id
WHERE st.stop_id = 12345

But the query takes a long time per stop.

I have indexes on:

routes (route_id)
stops (stop_id)
trips (trip_id, service_id, route_id)
stop_times (trip_id, stop_id)

Apart from doubling the size of my SQLite database, it hasn't done a great deal for the speed.

Does anyone know of a faster way to retrieve the values I require at a reasonable speen on an android device?

Thanks in advance.

Solution

This sorted it for those who are interested. It has gone from 7 seconds per query to less than a second for 10 queries.

select distinct rt.route_short_name
from routes rt, trips tr, stop_times st
where rt.route_id = tr.route_id
and tr.trip_id = st.trip_id
and st.stop_id =

Regards