SQL> select * from (select block_id ,segment_name from dba_extents where file_id= 5 order by 1) where rownum =3;


no rows selected

SQL> select * from (select block_id ,segment_name from dba_extents where file_id=5 order by 1) where rownum <3;

  BLOCK_ID SEGMENT_NAME
---------- ---------------
         9 REGIONS
        17 REG_ID_PK