select * from t where object_id <5;
Elapsed: 00:00:00.04
Execution Plan
----------------------------------------------------------
Plan hash value: 2486998213
----------------------------------------------------------------------------------------------
| Id  | Operation                   | Name           | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |                |    12 |  2484 |    14   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T              |    12 |  2484 |    14   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IDX1_OBJECT_ID |   689 |       |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("OBJECT_ID"<5)
Note
-----
   - dynamic sampling used for this statement (level=2)
Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          5  consistent gets
          0  physical reads
          0  redo size
       1470  bytes sent via SQL*Net to client
        384  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          3  rows processed


直接索引
select object_id from t where object_id<5;  
Elapsed: 00:00:00.01
Execution Plan
----------------------------------------------------------
Plan hash value: 1056850546
-----------------------------------------------------------------------------------
| Id  | Operation        | Name           | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT |                |    12 |   156 |     3   (0)| 00:00:01 |
|*  1 |  INDEX RANGE SCAN| IDX1_OBJECT_ID |    12 |   156 |     3   (0)| 00:00:01 |
-----------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - access("OBJECT_ID"<=5)
Note
-----
   - dynamic sampling used for this statement (level=2)
Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          3  consistent gets
          0  physical reads
          0  redo size
        466  bytes sent via SQL*Net to client
        384  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          4  rows processed
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