-- create a configuration favoring a full table scan and create a stored outline ;)
ALTER SESSION SET optimizer_index_cost_adj = 10000 ;
ALTER SESSION SET optimizer_index_caching = 1 ;
ALTER SESSION SET db_file_multiblock_read_count = 32 ;
ALTER SESSION SET optimizer_mode = all_rows ;

alter session set create_stored_outlines = TRUE;
CREATE OR REPLACE OUTLINE ol_tong FOR category hr_outlines ON
SELECT count(DISTINCT line)
FROM t1 WHERE owner = 'SYS' ;
alter session set create_stored_outlines=FALSE;

alter session set use_stored_outlines=hr_outlines;
set autotrace traceonly explain

SQL> SELECT count(DISTINCT line)
  2  FROM t1 WHERE owner = 'SYS' ;

Execution Plan
----------------------------------------------------------
Plan hash value: 3946799371
---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |    11 |  2544   (1)| 00:00:26 |
|   1 |  SORT GROUP BY     |      |     1 |    11 |            |          |
|*  2 |   TABLE ACCESS FULL| T1   | 17143 |   184K|  2544   (1)| 00:00:26 |			<- opps a fts??
---------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - filter("OWNER"='SYS')

Note
-----
   - outline "OL_TONG" used for this statement										<- tiny little note here :)

SQL> SELECT /*+ go_faster */ count(DISTINCT line)
  2  FROM t1 WHERE owner = 'SYS' ;

Execution Plan
----------------------------------------------------------
Plan hash value: 3456146945
---------------------------------------------------------------------------------------
| Id  | Operation                    | Name   | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |        |     1 |    11 |  1150   (1)| 00:00:12 |
|   1 |  SORT GROUP BY               |        |     1 |    11 |            |      |
|   2 |   TABLE ACCESS BY INDEX ROWID| T1     | 17143 |   184K|  1150   (1)| 00:00:12 |
|*  3 |    INDEX RANGE SCAN          | NUI_T1 | 17167 |       |    43   (3)| 00:00:01 |	<- this time cbo chooses a better plan 
---------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   3 - access("OWNER"='SYS')