在Oracle 9i引入跳跃式扫描的索引访问方法之前，查询只能在有限条件下使用该索引。除非在WHERE子句中对第一列指定一个值，否则就不能使用这个索引键进行一次范围扫描。

示例：对组合索引empt_id1(empno,ename,deptno)的测试

SQL> explain plan for select * from empt where empno=7369 and ename='SMITH' and

deptno=20;

已解释。

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT

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

Plan hash value: 1829075880

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

--------

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

me     |

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

--------

PLAN_TABLE_OUTPUT

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

|   0 | SELECT STATEMENT            |          |     1 |    87 |     2   (0)| 00

:00:01 |

|   1 |  TABLE ACCESS BY INDEX ROWID| EMPT     |     1 |    87 |     2   (0)| 00

:00:01 |

|*  2 |   INDEX RANGE SCAN          | EMPT_ID1 |     1 |       |     1   (0)| 00

:00:01 |

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

--------

PLAN_TABLE_OUTPUT

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

Predicate Information (identified by operation id):

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

   2 - access("EMPNO"=7369 AND "ENAME"='SMITH' AND "DEPTNO"=20)

Note

-----

   - dynamic sampling used for this statement

已选择18行。

SQL> explain plan for select * from empt where empno=7369;

已解释。

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT

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

Plan hash value: 1829075880

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

--------

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

me     |

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

--------

PLAN_TABLE_OUTPUT

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

|   0 | SELECT STATEMENT            |          |     1 |    87 |     2   (0)| 00

:00:01 |

|   1 |  TABLE ACCESS BY INDEX ROWID| EMPT     |     1 |    87 |     2   (0)| 00

:00:01 |

|*  2 |   INDEX RANGE SCAN          | EMPT_ID1 |     1 |       |     1   (0)| 00

:00:01 |

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

--------

PLAN_TABLE_OUTPUT

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

Predicate Information (identified by operation id):

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

   2 - access("EMPNO"=7369)

Note

-----

   - dynamic sampling used for this statement

已选择18行。

SQL> explain plan for select * from empt where deptno=20;

已解释。

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT

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

Plan hash value: 1497070856

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

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

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

|   0 | SELECT STATEMENT  |      |     5 |   435 |     3   (0)| 00:00:01 |

|*  1 |  TABLE ACCESS FULL| EMPT |     5 |   435 |     3   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

PLAN_TABLE_OUTPUT

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

   1 - filter("DEPTNO"=20)

Note

-----

   - dynamic sampling used for this statement

已选择17行。

注意：在Oracle 9i之前，只有在使用到索引的前导引时才可使用组合索引。