hint失效的情况

16:16:34 sys@prodadg1>select /*+ index(dept idx_dept_loc) */ * from scott.dept where loc='CHICAGO';
Elapsed: 00:00:00.00
Execution Plan
----------------------------------------------------------
Plan hash value: 3511320296
--------------------------------------------------------------------------------------------
| Id  | Operation                   | Name         | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |              |     1 |    20 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| DEPT         |     1 |    20 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IDX_DEPT_LOC |     1 |       |     1   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("LOC"='CHICAGO')
Statistics
----------------------------------------------------------
        167  recursive calls
          0  db block gets
         35  consistent gets
          0  physical reads
          0  redo size
        554  bytes sent via SQL*Net to client
        419  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          6  sorts (memory)
          0  sorts (disk)
          1  rows processed

16:17:18 sys@prodadg1>select /*+ index(dept idx_dept_loc) */ * from scott.dept where deptno=10;
Elapsed: 00:00:00.01
Execution Plan
----------------------------------------------------------
Plan hash value: 4024456447
--------------------------------------------------------------------------------------------
| Id  | Operation                   | Name         | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |              |     1 |    20 |     2   (0)| 00:00:01 |
|*  1 |  TABLE ACCESS BY INDEX ROWID| DEPT         |     1 |    20 |     2   (0)| 00:00:01 |
|   2 |   INDEX FULL SCAN           | IDX_DEPT_LOC |     4 |       |     1   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter("DEPTNO"=10)
Statistics
----------------------------------------------------------
        218  recursive calls
          0  db block gets
         42  consistent gets
          0  physical reads
          0  redo size
        556  bytes sent via SQL*Net to client
        419  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          6  sorts (memory)
          0  sorts (disk)
          1  rows processed


16:15:03 sys@prodadg1>desc scott.dept;
 Name                                                                       Null?    Type
 -------------------------------------------------------------------------- -------- --------------------------------------------------
 DEPTNO                                                                     NOT NULL NUMBER(2)
 DNAME                                                                               VARCHAR2(14)
 LOC                                                                                 VARCHAR2(13)

3,hint失效
16:16:58 sys@prodadg1>select /*+ index(dept idx_dept_loc) */ * from scott.dept where deptno=10;
Elapsed: 00:00:00.01
Execution Plan
----------------------------------------------------------
Plan hash value: 2852011669
---------------------------------------------------------------------------------------
| Id  | Operation                   | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |         |     1 |    20 |     1   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| DEPT    |     1 |    20 |     1   (0)| 00:00:01 |
|*  2 |   INDEX UNIQUE SCAN         | PK_DEPT |     1 |       |     0   (0)| 00:00:01 |
---------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("DEPTNO"=10)
Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          2  consistent gets
          1  physical reads
          0  redo size
        464  bytes sent via SQL*Net to client
        408  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed








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