CREATE TABLE station (name VARCHAR, station_id VARCHAR)
CREATE TABLE train_station (station_id VARCHAR)

Show the station name with greatest 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 LIMIT 1
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 NULLS LAST LIMIT 1