CREATE OR REPLACE FUNCTION st() RETURNS varchar(255) AS $$
DECLARE
	cur CURSOR FOR SELECT station_id, train_id, arrive_time, departure_time FROM schedules;
	cur2 CURSOR FOR SELECT station_id, train_id, arrive_time, departure_time FROM schedules;
	curmax integer;
	maximum integer;
	maxstation varchar(255);
	_count integer;
	_station_name varchar(255);
	_station_name2 varchar(255);
	_train_code varchar(50);
	_train_code2 varchar(50);
	_arrive_time time;
	_arrive_time2 time;
	_departure_time time;
	_departure_time2 time;
BEGIN
	OPEN cur;
	OPEN cur2;
	execute 'SELECT count(*) FROM schedules' into _count;
	maximum := 1;
	maxstation := 'Везде равно';

	FOR i IN 1.._count LOOP
		curmax := 1;
		FETCH NEXT FROM cur INTO _station_name, _train_code, _arrive_time, _departure_time;
		IF _arrive_time = null OR _departure_time = null THEN
			CONTINUE;
		END IF;
		FOR j IN 1.._count LOOP
			FETCH NEXT FROM cur2 INTO _station_name2, _train_code2, _arrive_time2, _departure_time2;
			IF _arrive_time2 = null OR _departure_time = null THEN
				CONTINUE;
			END IF;
			IF _train_code <> _train_code2 THEN
				IF _arrive_time <= _arrive_time2 AND _departure_time >= _arrive_time2 THEN
					curmax := curmax + 1;
				ELSIF _arrive_time <= _departure_time2 AND _departure_time >= _departure_time2 THEN
					curmax := curmax + 1;
				END IF;
			END IF;
		END LOOP;
		IF curmax > maximum THEN
			maximum := curmax;
			maxstation := _station_name;
		END IF;
	END LOOP;
	return maxstation;
END
$$ LANGUAGE plpgsql;

SELECT st();