More Variations on NOT IN problem

I have more variations on the use of NOT IN and NOT EXISTS; I ran both through the optimizer and got the same result; the first select is extrememly slow but returns the correct answer; the second runs fast but doesn't return any rows:

(1):

explain plan set statement_id = 'SELECT1' for
select distinct b.crr_itn_plnd_glc_cd from carrier_itinerary b   where not exists
    (select distinct a.op_rtg_glc_cd from oplan_force_rqmt_loc a

        where a.op_pln_id = '120AX'  and
         a.op_rtg_glc_cd = b.crr_itn_plnd_glc_cd
         )

(2):

explain plan set statement_id = 'SELECT2' for
select distinct b.crr_itn_plnd_glc_cd from carrier_itinerary b

   where b.crr_itn_plnd_glc_cd NOT IN

     (select distinct a.op_rtg_glc_cd from oplan_force_rqmt_loc a
         where a.op_pln_id = '120AX'
     )

Both return the following from the optimizer:

ID   OPERATION           OPTIONS    OBJECT_NAME                Parent_ID   POSITION
--   ------------------  --------   ---------------------      ----        -----  
0    SELECT STATEMENT 								                                             	11
1     SORT               UNIQUE                                 0            1
2     FILTER                                                    1            1
3     TABLE ACCESS       FULL        CARRIER_ITINERARY          2            1
4     TABLE ACCESS       BY ROWID    OPLAN_FORCE_RQMT_LOC       2            2
5     INDEX              RANGE SCAN  pk_opfrq_loc               4            1

6 rows selected.

SQL>   Any Ideas???? Received on Wed Jul 26 1995 - 00:00:00 CEST