Performance in ORDER BY

Hello everybody!!

  We have a SELECT running over our database. We only need several registers of a table of 800.000 values. In the SELECT when we put in comments the ORDER BY T.START_TIME DESC line, the instruction is executed in 7 seconds, but if we use the ORDER BY line, the execution goes to 8 minutes.

  I would appreciate any tip very much, cos I am desperate with it.

  Thanks in advance.

 Abel S.

      SELECT CCID,GROUP_ID, ....(other fields)
      FROM (
        SELECT S.CCID, S.GROUP_ID, ...., ROWNUM AS RN
        FROM SITEINFO S,TIMESTMP T, ADDEF A, UNIT U
        WHERE A.TYPE ='DI' AND  T.STATUS = 'C'  AND  T.USER_ID IS NULL

        ORDER BY T.START_TIME DESC
      )     
      WHERE RN BETWEEN 4051 AND 4125;