CREATE TABLE train (train_id DECIMAL, name TEXT, time TEXT, service TEXT)
CREATE TABLE train_station (train_id DECIMAL, station_id DECIMAL)
CREATE TABLE station (station_id DECIMAL, name TEXT, annual_entry_exit DECIMAL, annual_interchanges DECIMAL, total_passengers DECIMAL, location TEXT, main_services TEXT, number_of_platforms DECIMAL)

Show the location with most number of train stations.
SELECT location FROM station GROUP BY location ORDER BY COUNT(*) DESC LIMIT 1
SELECT "location" FROM "station" GROUP BY "location" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1