It's not going to work. You cannot reference calculated fields in consequent calculations in the same list. You can use derived table

SELECT *, ABS(dt1.x2-dt2.y2) AS dx ;
  FROM ( ;
select temp1.*,nodes.x as x2, nodes.y as y2, 
	from UPDNETATR!xydata nodes ;
	right outer join temp1 ;
	on  nodes.n = temp1.b;
	where st_name <> ' ' ;
	order by temp1.st_name ;
       ) dt1 

>Yes it is:
>BTW the result contains x2 and Y2 :-)
>of course if you didn't have X1 in Temp1
>

>select temp1.*,nodes.x as x2, nodes.y as y2, ABS(nodes.x-nodes.y) AS dx;
>	from UPDNETATR!xydata nodes ;
>	right outer join temp1 ;
>	on  nodes.n = temp1.b;
>	where st_name <> ' ' ;
>	order by temp1.st_name
>