SELECT
A.name as passengerName1,
B.name as passengerName2, COUNT(*) as count
FROM
(SELECT DISTINCT name, passenger, trip FROM Pass_in_trip INNER JOIN Passenger ON Pass_in_trip.passenger=
Passenger.id) as A
INNER JOIN
(SELECT DISTINCT name, passenger, trip FROM Pass_in_trip INNER JOIN Passenger ON Pass_in_trip.passenger=
Passenger.id) as B
on A.trip = B.trip and A.passenger < B.passenger
GROUP BY passengerName1, passengerName2
HAVING count >= 2