I’m not a great user of iSeries Navigator for DB management but if I’m not wrong it uses SQL to create indexes and you can’t create “selection” indexes with SQL.
However, if you want to have a filtered set of records through SQL, you’d probably want to create an SQL view. An example is:
Create View MYLIB/MYVIEW As
Where (ICStat = ‘I’ And ICTIPC = 1)