System altered.

SQL> set autotrace traceonly;
  ----查询一个范围的执行计划----
SQL> select * from jack where object_id>1000 and object_id<2000;

9880 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 949574992

--------------------------------------------------------------------------
| Id  | Operation      | Name | Rows  | Bytes | Cost (%CPU)| Time    |
--------------------------------------------------------------------------
|  0 | SELECT STATEMENT  |    |  9657 |  914K|  1824  (1)| 00:00:22 |
|*  1 |  TABLE ACCESS FULL| JACK |  9657 |  914K|  1824  (1)| 00:00:22 |
--------------------------------------------------------------------------

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

  1 - filter("OBJECT_ID"<2000 AND "OBJECT_ID">1000)

Statistics
----------------------------------------------------------
      0  recursive calls
      0  db block gets
    10993 consistent gets
    10340 physical reads
      0  redo size
  471945 bytes sent via SQL*Net to client
    7657  bytes received via SQL*Net from client
    660  SQL*Net roundtrips to/from client
      0  sorts (memory)
      0  sorts (disk)
    9880  rows processed      ----注意，object_id上是有索引的，但是这里并没有使用索引，而是使用了全表扫描。

SQL> alter system flush buffer_cache;

System altered.

 ----强制走索引，查看执行计划----
SQL> select /*+ index(jack jack_ind) */ * from jack where object_id>1000 and object_id<2000;

9880 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 2860868395

----------------------------------------------------------------------------------------
| Id  | Operation            | Name    | Rows  | Bytes | Cost (%CPU)| Time    |
----------------------------------------------------------------------------------------
|  0 | SELECT STATEMENT        |          |  9657 |  914K|  9683    (1)| 00:01:57 |
|  1 |  TABLE ACCESS BY INDEX ROWID| JACK    |  9657 |  914K|  9683    (1)| 00:01:57 |
|*  2 |  INDEX RANGE SCAN        | JACK_IND |  9657 |      |    24    (0)| 00:00:01 |
----------------------------------------------------------------------------------------

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

  2 - access("OBJECT_ID">1000 AND "OBJECT_ID"<2000)