--查看表上的数据分布情况，可以确定，对于索引列owner，针对scott以及bi的普通查询，一定会使用索引。Yumiko@Sunny >select owner,count(*) from test01 group by owner;OWNER                            COUNT(*)
------------------------------ ----------
SCOTT                                  11
BI                                      8
SYS                                 22909--为owner列创建普通b-tree索引
Yumiko@Sunny >create index btree_owner on test01(owner);
Index created.--验证创建的索引
Yumiko@Sunny >select a.INDEX_NAME INDEX_NAME,b.INDEX_TYPE INDEX_TYPE,a.TABLE_NAME TABLE_NAME,COLUMN_NAME,STATUS2  from user_ind_columns a,user_indexes b3  where a.INDEX_NAME=b.INDEX_NAME and a.table_name='TEST01';INDEX_NAME      INDEX_TYPE      TABLE_NAME      COLUMN_NAME          STATUS
--------------- --------------- --------------- -------------------- --------
BTREE_OWNER     NORMAL          TEST01          OWNER                VALID--利用索引列，针对列值为BI，进行普通查询--与预想一样，这里用到了索引扫描
Yumiko@Sunny >select * from test01 where owner='BI';
8 rows selected.Execution Plan
----------------------------------------------------------
Plan hash value: 725909888
-------------------------------------------------------------------------------------------
| Id  | Operation                   | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |             |     1 |    92 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST01      |     1 |    92 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | BTREE_OWNER |     1 |       |     1   (0)| 00:00:01 |
-------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------2 - access("OWNER"='BI')Statistics
----------------------------------------------------------0  recursive calls0  db block gets5  consistent gets16  physical reads0  redo size2010  bytes sent via SQL*Net to client469  bytes received via SQL*Net from client2  SQL*Net roundtrips to/from client0  sorts (memory)0  sorts (disk)8  rows processed
--清空buffer_cache缓冲区，避免影响后续操作对于物理读的观察。
Yumiko@Sunny >alter system flush buffer_cache;
System altered.--使用UPPER函数进行条件过滤，并观察执行计划
--通过执行计划，可以明显看出，未使用索引扫描，进而导致大量的物理读操作。Yumiko@Sunny >select * from test01 where UPPER(owner)='BI';
8 rows selected.Execution Plan
----------------------------------------------------------
Plan hash value: 262542483
----------------------------------------------------------------------------
| Id  | Operation         | Name   | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |        |   229 | 21068 |   158   (1)| 00:00:02 |
|*  1 |  TABLE ACCESS FULL| TEST01 |   229 | 21068 |   158   (1)| 00:00:02 |
----------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------1 - filter(UPPER("OWNER")='BI')Statistics
----------------------------------------------------------1  recursive calls0  db block gets697  consistent gets692  physical reads0  redo size1583  bytes sent via SQL*Net to client469  bytes received via SQL*Net from client2  SQL*Net roundtrips to/from client0  sorts (memory)0  sorts (disk)8  rows processed

--在索引列上建立函数索引Yumiko@Sunny >create index func_owner on test01(UPPER(owner));
Index created.--查看并验证建立的函数索引--需要注意的，由于此索引是基于函数建立的，因此columns一列无法显示真正的列名，可以通过user_ind_expressions视图查看
Yumiko@Sunny >select a.INDEX_NAME INDEX_NAME,b.INDEX_TYPE INDEX_TYPE,a.TABLE_NAME TABLE_NAME,COLUMN_NAME,STATUS2  from user_ind_columns a,user_indexes b3  where a.INDEX_NAME=b.INDEX_NAME and a.table_name='TEST01';INDEX_NAME      INDEX_TYPE                TABLE_NAME      COLUMN_NAME          STATUS
--------------- ------------------------- --------------- -------------------- --------
FUNC_OWNER      FUNCTION-BASED NORMAL     TEST01          SYS_NC00014$         VALID
BTREE_OWNER     NORMAL                    TEST01          OWNER                VALIDYumiko@Sunny >select * from user_ind_expressions where INDEX_NAME='FUNC_OWNER';INDEX_NAME      TABLE_NAME      COLUMN_EXPRESSION              COLUMN_POSITION
--------------- --------------- ------------------------------ ---------------
FUNC_OWNER      TEST01          UPPER("OWNER")                               1--打开会话追踪
Yumiko@Sunny >set autotrace trace;

--清空buffer_cache缓冲区
Yumiko@Sunny >alter system flush buffer_cache;
System altered.--再次使用UPPER函数进行条件查询，此时执行计划使用索引扫描，进而物理读明显降低。
Yumiko@Sunny >select * from test01 where upper(owner)='BI';
8 rows selected.Execution Plan
----------------------------------------------------------
Plan hash value: 939299437
------------------------------------------------------------------------------------------
| Id  | Operation                   | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |            |   229 | 21068 |    19   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST01     |   229 | 21068 |    19   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | FUNC_OWNER |    92 |       |    16   (0)| 00:00:01 |
------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------2 - access(UPPER("OWNER")='BI')Statistics
----------------------------------------------------------32  recursive calls0  db block gets8  consistent gets19  physical reads0  redo size1583  bytes sent via SQL*Net to client469  bytes received via SQL*Net from client2  SQL*Net roundtrips to/from client0  sorts (memory)0  sorts (disk)8  rows processed