【SQL】查找数据的方式 (二)

如果表查询中所有的列都包括在了索引中，就有可能使用FFS，当然也可以使用hint来选择FFS。下面看看使用不同方式访问索引的例子：

SQL> create index idx_un_tset_ownid_dataid on un_test (owner,data_object_id);

Index created.

Elapsed: 00:00:00.96

SQL> select owner ,data_object_id from un_test

  2  where data_object_id >5;

6891 rows selected.

Elapsed: 00:00:00.06

Execution Plan

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

Plan hash value: 287826149

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

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

|   0 | SELECT STATEMENT     |                          |  6913 | 55304 |    32   (4)| 00:00:01 |

|*  1 |  INDEX FAST FULL SCAN| IDX_UN_TSET_OWNID_DATAID |  6913 | 55304 |    32   (4)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

   1 - filter("DATA_OBJECT_ID">5)

Statistics

          1  recursive calls

          0  db block gets

        602  consistent gets

        135  physical reads

          0  redo size

          ..........

          0  sorts (memory)

          0  sorts (disk)

       6891  rows processed

  2   where data_object_id =5;

no rows selected

Elapsed: 00:00:00.00

Plan hash value: 1786681723

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

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

|   0 | SELECT STATEMENT |                          |     1 |     8 |    21   (0)| 00:00:01 |

|*  1 |  INDEX SKIP SCAN | IDX_UN_TSET_OWNID_DATAID |     1 |     8 |    21   (0)| 00:00:01 |

   1 - access("DATA_OBJECT_ID"=5)

       filter("DATA_OBJECT_ID"=5)

         15  consistent gets

          0  physical reads

           。。。。。。

          0  rows processed

SQL> select object_id from un_test where object_id = 5;

Elapsed: 00:00:00.01

Plan hash value: 333614268

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

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

|   0 | SELECT STATEMENT  |            |     1 |     5 |     1   (0)| 00:00:01 |

|*  1 |  INDEX UNIQUE SCAN| I_TEST_UNI |     1 |     5 |     1   (0)| 00:00:01 |

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

   1 - access("OBJECT_ID"=5)

          2  consistent gets

           。。。。。

          1  rows processed

SQL> select /*+ index_ffs(a)*/ owner,data_object_id from un_test a

  2  where wner = 'SYS';

23021 rows selected.

Elapsed: 00:00:00.12

|   0 | SELECT STATEMENT     |                          |  2668 | 21344 |    32   (4)| 00:00:01 |

|*  1 |  INDEX FAST FULL SCAN| IDX_UN_TSET_OWNID_DATAID |  2668 | 21344 |    32   (4)| 00:00:01 |

   1 - filter("OWNER"='SYS')

       1674  consistent gets

          。。。。。。。

      23021  rows processed

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

SQL> SELECT /* INDEX(A)*/ OWNER,DATA_OBJECT_ID FROM UN_TEST A

  2  WHERE WNER ='SYS';

Plan hash value: 3998526102

|   0 | SELECT STATEMENT |                          |  2668 | 21344 |     8   (0)| 00:00:01 |

|*  1 |  INDEX RANGE SCAN| IDX_UN_TSET_OWNID_DATAID |  2668 | 21344 |     8   (0)| 00:00:01 |

   1 - access("OWNER"='SYS')

       1586  consistent gets

          。。。。。

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

SQL> select /*+ index (a idx_un_test_ownid_dataid)*/ count(*) from un_test a

  2  where data_object_id = 5;

Plan hash value: 1636324484

|   0 | SELECT STATEMENT |                          |     1 |     2 |    21   (0)| 00:00:01 |

|   1 |  SORT AGGREGATE  |                          |     1 |     2 |            |          |

|*  2 |   INDEX SKIP SCAN| IDX_UN_TSET_OWNID_DATAID |     1 |     2 |    21   (0)| 00:00:01 |

   2 - access("DATA_OBJECT_ID"=5)

---位图索引。。

SQL> select /*+ index(a idx_type_bit)*/ * from un_test a

  2  where a.object_type ='TABLE';

2921 rows selected.

Elapsed: 00:00:00.05

Plan hash value: 4191918535

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

|   0 | SELECT STATEMENT             |              |  1779 |   161K|   194   (0)| 00:00:03 |

|   1 |  TABLE ACCESS BY INDEX ROWID | UN_TEST      |  1779 |   161K|   194   (0)| 00:00:03 |

|   2 |   BITMAP CONVERSION TO ROWIDS|              |       |       |            |          |

|*  3 |    BITMAP INDEX SINGLE VALUE | IDX_TYPE_BIT |       |       |            |          |

   3 - access("A"."OBJECT_TYPE"='TABLE')

        347  consistent gets

          1  physical reads

       2921  rows processed