SELECT *
    FROM (SELECT T.*, ROWNUM ROWNUM_
            FROM (SELECT A.*
                    FROM table A
                   ORDER BY A.FieldName DESC) T
           WHERE ROWNUM < endNum) T
   WHERE T.ROWNUM_ > startNum

SELECT X.*
  FROM (SELECT ROW_NUMBER() OVER(ORDER BY FieldName DESC) AS ROW_NO,
               A.*
          FROM table A) X
 WHERE X.ROW_NO <= 41
   AND X.ROW_NO >= 21;