UPDATE ( 
  SELECT ORDERED PARALLEL(t 4)
      t.I_ID     t_I_ID 
    , t.s_dte    t_s_dte 
    , t.e_dte    t_end_dte 
    , s.I_ID     S_I_ID 
    , s.s_dte    t_s_dte 
    , TO_DATE(DECODE(r_cde,'U','&PREV_day_DTE','&SYS_DTE'), 
                    'YYYYMMDD') e_dte 
  FROM 
       TMP_HISTORY s, 
       HISTORY t
  WHERE 
        s.I_ID = t.I_ID 
  AND   t.e_dte = TO_DATE('20091231','YYYYMMDD') 
  AND   s.r_cde IN ('U','D') 
  ) tp
  SET 
      t_end_dte = e_dte

15:00:15 SQL> set autot trace exp
15:00:23 SQL> update a set navn = 'lars' ;

1 row updated.

Elapsed: 00:00:00.00

Execution Plan
----------------------------------------------------------
Plan hash value: 3279622862

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | UPDATE STATEMENT   |      |     1 |     4 |     3   (0)| 00:00:01 |
|   1 |  UPDATE            | A    |       |       |            |          |
|   2 |   TABLE ACCESS FULL| A    |     1 |     4 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------

15:00:36 SQL>