Manage to get the right combination

SELECT distinct R1.FlightNum, R1.FromCityCode, R1.ToCityCode

FROM ...

My code is not the result that should be

Mate

Have tried it and it came with an error

ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list

SQL state: 42P10

Thanks Young

I am totally new to SQL and i cant figure out what is wrong. Please if you could post the modify version of the query i've send....

Have tried this query but seems not working

QUERY

------

SELECT distinct R1.FlightNum, R1.FromCityCode, R2.ToCityCode

FROMFlights R1, Flights R2

WHERE(R1.FromCityCode = R2.ToCityCode)

AND(R1.FlightNum < R2.FlightNum)

ORDER BYR1.FlightNum, R1.FromCityCode, R2.ToCityCode

TABLE

------

CREATE TABLE flights

(

flightnum numeric(2) NOT NULL,

...