Thanks Sergey.

No, that didn't work. I seem to have cracked it with:

...
  LEFT JOIN RF1 ;
    On	NET.Operator  == RF1.Operator ;
    and (    NET.Route == RF1.ERoute ;
      	 or EMPTY( RF1.ERoute) ) ;
...

>>Sorry Sergey, I don't understand. I'm not intending to do "strange experiments". Your reply is very vague. I told you originally had that clause in, and got wrong results, and this was before I was advised to LEFT JOIN.
>>
>>Is there a solution to this or is the whole thread too hard to understand?
>Try
>

>SELECT DISTINCT NET.Operator, NET.Route, NET.Start_Date, NET.End_Date, NET.RorF, NET.Passengers, ;
>	IIF( NET.Route == NET.Mcl_Rte, "    ", NET.Mcl_Rte) as ContrNum, NET.Family, ;
>	0000000 AS CurrPass, 0000000 AS PrevPass, op.Desc as OpDesc, ;
>	NVL(RF1.ServType, "?") as ServeType ;	
>  FROM NotETM NET ;
>    JOIN Operator op ;
>      On NET.Operator == op.Code ;
>    LEFT JOIN RF1 ;
>      On  NET.Operator == RF1.Operator ;
>      and NET.Route    == RF1.ERoute ;
>  WHERE (	 (	m.ldStartCurr BETWEEN NET.Start_date AND NET.End_date) ; ...
>