ANY IDEA ON USING INDEX FOR ORDER BY

ANY IDEA ON USING INDEX FOR ORDER BY The optimizer dos not use index on refno for order by when I add t.fileid BETWEEN "BK7180IN" AND "BK7200IN" in where clause. I tried update statistics but nothing changed. fileid CHAR(8) refno INTEGER And sqexplain.out is : QUERY: ------ SELECT * FROM transaction t WHERE t.fileid BETWEEN "BK7180IN" AND "BK7200IN" ORDER BY t.refno Estimated Cost: 3 Estimated # of Rows Returned: 1 Temporary Files Required For: Order By 1) crx.t: INDEX PATH (1) Index Keys: fileid Lower Index Filter: crx.t.fileid >= 'BK7180IN' Upper Index Filter: crx.t.fileid <= 'BK7200IN'