SELECT TP.strFirstName, 
    TP.strLastName, 
    SUM(TF.intMilesFlown) AS TotalMilesFlown
FROM TPassengers AS TP
JOIN TFlightPassengers AS TFP
     ON TP.intPassengerID = TFP.intPassengerID
JOIN TFlights AS TF
     ON TFP.intFlightID = TF.intFlightID		  
GROUP BY TP.strLastName, 
    TP.strFirstName
ORDER BY TotalMilesFlown DESC
LIMIT 1;

SELECT TOP 1 TP.strFirstName, 
    TP.strLastName, 
    sum(TF.intMilesFlown)
FROM TPassengers AS TP
JOIN TFlightPassengers AS TFP
     ON TP.intPassengerID = TFP.intPassengerID
JOIN TFlights AS TF
     ON TFP.intFlightID = TF.intFlightID          
GROUP BY TP.strLastName, 
    TP.strFirstName
ORDER BY SUM(TF.intMilesFlown) DESC;