Your query worked like a charm. I did make two changes, because my previous example was not quite correct. I only want rows in the result set that have data in fld2. Thanks!

select FldID, Fld2 from Tbl2 where Fld2<>SPACE(10) ;
UNION ;
select FldID, Fld2 from Tbl1 where exists (select 1 from Tbl2 where Fld2 = space(10) and FldID = Tbl1.FldID) and Fld2<>SPACE(10)