Show the name for all train stations.
select name from station
Order those names in descending order of the number of trains.
select t2.name from train_station as t1 join station as t2 on t1.station_id = t2.station_id group by t1.station_id order by count(*) desc
Which one has the most?
select t2.name from train_station as t1 join station as t2 on t1.station_id = t2.station_id group by t1.station_id order by count(*) desc limit 1