Cost decrease ?

From: astalavista <nobody_at_nowhere.com>
Date: Wed, 22 Aug 2007 21:35:48 +0200
Message-ID: <46cc9011$0$427$426a74cc@news.free.fr>

Hi,

In the explain plan below
why the intermediate cost for index full scan is 5979 and the final cost is 65.
Something I did'nt understand ?

Thanks in advance

SQL> explain plan for
2 SELECT COUNT (*)
3 FROM wx_synd_data_f vnt, wc_prodcat_dh prd_dh 4 WHERE vnt.prod_wid = prd_dh.prod_wid AND prd_dh.usage_cd = 'Ville' 5 /

Explained.

Elapsed: 00:00:00.00
SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT

| 0 | SELECT STATEMENT | | 1 |
13 | 65 (16)|
| 1 | SORT AGGREGATE | | 1 |

13 |            |


|   2 |   MERGE JOIN                    |                        |  9808M| 

118G|    65  (16)|


|   3 |    INDEX FULL SCAN              | WX_SYND_DATA_F_F8      |    12M| 

34M|  5979  (12)|
|*  4 |    SORT JOIN                    |                        |  1095 | 
10950 |     5  (60)|


|   5 |     TABLE ACCESS BY INDEX ROWID | WC_PRODCAT_DH          |  1095 | 

10950 |     3  (34)|


|   6 |      BITMAP CONVERSION TO ROWIDS|                        |       | 

|            |

PLAN_TABLE_OUTPUT

|*  7 |       BITMAP INDEX SINGLE VALUE | WC_PRODCAT_DH_BMX_M11  |       | 


|            |

-----------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

   4 - access("VNT"."PROD_WID"="PRD_DH"."PROD_WID")
       filter("VNT"."PROD_WID"="PRD_DH"."PROD_WID")
   7 - access("PRD_DH"."USAGE_CD"='Ville')

20 rows selected.

Elapsed: 00:00:00.02 Received on Wed Aug 22 2007 - 14:35:48 CDT