Oracle SAMPLE语句学习（四）SAMPLE扫描和HINT的关系

Oracle的文档上描述，当不包含SAMPLE语句的时候，可以使用HINT来指定执行计划，实际上即使包含SAMPLE语句，HINT也是生效的。

SQL> SELECT OBJECT_ID FROM T SAMPLE (1) WHERE WNER = USER;

OBJECT_ID

----------

60607

70958

执行计划

----------------------------------------------------------

Plan hash value: 3630032853

-------------------------------------------------------------------------------------------

| Id  | Operation                   | Name        | Rows  | Bytes | Cost (%CPU)| Time     |

-------------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT            |             |    22 |   506 |     6   (0)| 00:00:01 |

|   1 |  TABLE ACCESS BY INDEX ROWID| T           |    22 |   506 |     6   (0)| 00:00:01 |

|*  2 |   INDEX RANGE SCAN          | IND_T_OWNER |    22 |       |     5   (0)| 00:00:01 |

-------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

2 - access("OWNER"=USER@!)

filter(ORA_HASH(ROWID,0,2211694651,'SYS_SAMPLE',0)<42949673)

统计信息

----------------------------------------------------------

0  recursive calls

0  db block gets

6  consistent gets

4  physical reads

0  redo size

452  bytes sent via SQL*Net to client

385  bytes received via SQL*Net from client

2  SQL*Net roundtrips to/from client

0  sorts (memory)

0  sorts (disk)

2  rows processed

SQL> SELECT /*+ FULL(T) */ OBJECT_ID FROM T SAMPLE (1) WHERE WNER = USER;

未选定行

执行计划

----------------------------------------------------------

Plan hash value: 2767392432

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----------------------------------------------------------------------------

| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |

----------------------------------------------------------------------------

|   0 | SELECT STATEMENT    |      |    22 |   506 |   158   (2)| 00:00:02 |

|*  1 |  TABLE ACCESS SAMPLE| T    |    22 |   506 |   158   (2)| 00:00:02 |

----------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

1 - filter("OWNER"=USER@!)

统计信息

----------------------------------------------------------

1  recursive calls

0  db block gets

517  consistent gets

430  physical reads

0  redo size