Why is this query not using the index?

Question

check out this query:-
SELECT CUST_PO_NUMBER, HEADER_ID, ORDER_TYPE, PO_DATE
FROM TABLE1
WHERE STATUS = 'N'
and here's the explain plan:-
1     
2     -------------------------------------------------------------------------------------
3     | Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
4     -------------------------------------------------------------------------------------
5     | 0 | SELECT STATEMENT | | 2735K| 140M| 81036 (2)|
6     |* 1 | TABLE ACCESS FULL| TABLE1 | 2735K| 140M| 81036 (2)|
7     -------------------------------------------------------------------------------------
8     
9     Predicate Information (identified by operation id):
10     ---------------------------------------------------
11     
12     1 - filter("STATUS"='N')
There is already an index on this column, as is shown below:-
     INDEX_NAME INDEX_TYPE     UNIQUENESS     TABLE_NAME     COLUMN_NAME     COLUMN_POSITION
1     TABLE1_IDX2 NORMAL     NONUNIQUE     TABLE1      STATUS     1
2     TABLE1_IDX NORMAL     NONUNIQUE     TABLE1     HEADER_ID     1
So why is this query not using the index on the 'STATUS' Column?
I've already tried using optimizer hints and regathering the stats on the table, but the execution plan still remains the same, i.e. it still uses a FTS.
I have tried this command also:-
exec dbms_stats.gather_table_stats('GECS','GEPS_CS_SALES_ORDER_HEADER',method_opt=>'for all indexed columns size auto',cascade=>true,degree=>4);
inspite of this, the query is still using a full table scan.
The table has around 55 Lakh records, across 60 columns. And because of the FTS, the query is taking a long time to execute. How do i make it use the index?
Please help.
Edited by: user10047779 on Mar 16, 2010 6:55 AM

Answer 1

If the cardinality is really as skewed as that, you may want to look at putting a histogram on the column (sounds like it would be in order, and that you don't have one).
create table skewed_a_lot
as
   select
      case when mod(level, 1000) = 0 then 'N' else 'Y' end as Flag,
      level as col1
   from dual connect by level <= 1000000;
create index skewed_a_lot_i01 on skewed_a_lot (flag);
exec dbms_stats.gather_table_stats(user, 'SKEWED_A_LOT', cascade => true, method_opt => 'for all indexed columns size auto');Is an example.