tuning SQL statement...AUTOTRACE

I am trying to use autotrace utility to check the execution plan of table, and later I will create index to check whether the performance is improved.

SQL> conn sys/rock@rock as sysdba
Connected.
SQL> create table test as select * from all_objects;
Table created.

SQL> exec dbms_stats.gather_table_stats(ownname => 'SYS',tabname=>'TEST',force=>true);
PL/SQL procedure successfully completed.
SQL>
SQL> select count (*) from test;
COUNT(*)
----------
49771

SQL> desc test
Name
------------------------------------------------------------------
OWNER
OBJECT_NAME
SUBOBJECT_NAME
OBJECT_ID
DATA_OBJECT_ID
OBJECT_TYPE
CREATED
LAST_DDL_TIME
TIMESTAMP
STATUS
TEMPORARY
GENERATED
SECONDARY
SQL>
SQL> select count (distinct(data_object_id)) from test;
COUNT(DISTINCT(DATA_OBJECT_ID))
-------------------------------
3504

SQL> autotrace on;

SQL> select * from test where data_object_id=151596;
OWNER OBJECT_NAME OBJECT_ID
------------------------------ ------------------------------
RMAN2 TF_P 151596

Execution Plan
----------------------------------------------------------
Plan hash value: 1357081020
--------------------------------------------------------------------------
Id Operation Name Rows Bytes Cost (%CPU) Time
--------------------------------------------------------------------------
0 SELECT STATEMENT 1 93 154 (2) 00:00:02
* 1 TABLE ACCESS FULL TEST 1 93 154 (2) 00:00:02
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("DATA_OBJECT_ID"=151596)

Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
689 consistent gets
0 physical reads
0 redo size
1202 bytes sent via SQL*Net to client
381 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed

SQL> create index test_data_idx on test(data_object_id)
Index created.
SQL> select * from test where data_object_id=151596;
OWNER OBJECT_NAME OBJECT_ID
------------------------------ ------------------------------
RMAN2 TF_P 151596

Execution Plan
----------------------------------------------------------
Plan hash value: 2271528063
---------------------------------------------------------------------------------------------
Id Operation Name Rows Bytes Cost (%CPU) Time
---------------------------------------------------------------------------------------------
0 SELECT STATEMENT 1 93 2 (0) 00:00:01
1 TABLE ACCESS BY INDEX ROWID TEST 1 93 2 (0) 00:00:01
* 2 INDEX RANGE SCAN TEST_DATA_IDX 1 1 (0) 00:00:01
---------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("DATA_OBJECT_ID"=151596)

Statistics
----------------------------------------------------------
149 recursive calls
0 db block gets
28 consistent gets
1 physical reads
0 redo size
1206 bytes sent via SQL*Net to client
381 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
3 sorts (memory) 0 sorts (disk)
1 rows processed

Conclusion: By creating index the cost of CPU is improved from 154% to 2 %, because the row was accessed by INDEX ROWID.
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Explain plan Vs AUTOTRACE
http://www.oracle-base.com/articles/8i/ExplainPlanUsage.php