深入理解Oracle索引(15)：日期转换函数的格式参数大小写规则对函数索引的影响

     规则如下：

                      


     依据这个规则、只有 3 种输出：大写、小写、首字母大写
     
     测试如下：

sys@ORCL> select to_char(sysdate,'Month') from dual;

TO_CHAR(SYSDATE,'MONTH')
------------------------------------
June

sys@ORCL> select to_char(sysdate,'MOnth') from dual;

TO_CHAR(SYSDATE,'MONTH')
------------------------------------
JUNE

sys@ORCL> select to_char(sysdate,'month') from dual;

TO_CHAR(SYSDATE,'MONTH')
------------------------------------
june


     下面做个测试、确认这个规则对函数索引的影响：

sys@ORCL> drop table t purge;

Table dropped.

sys@ORCL> create table t as select object_id,sysdate+rownum as create_date from dba_objects where rownum<=5000;

Table created.

sys@ORCL> analyze table t compute statistics;

Table analyzed.

sys@ORCL> set autot trace exp
sys@ORCL> select * from t where to_char(create_date,'yyyy-mm-dd')='2011-06-02';

Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873

--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 50 | 500 | 5 (20)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T | 50 | 500 | 5 (20)| 00:00:01 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter(TO_CHAR(INTERNAL_FUNCTION("CREATE_DATE"),'yyyy-mm-dd')='20
11-06-02')

sys@ORCL> create index idx_t on t (to_char(create_date,'YYYY-MM-DD'));

Index created.

sys@ORCL> analyze index idx_t validate structure;

Index analyzed.

sys@ORCL> select * from t where to_char(create_date,'yyyy-mm-dd')='2013-06-02';

Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873

--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 50 | 500 | 5 (20)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T | 50 | 500 | 5 (20)| 00:00:01 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter(TO_CHAR(INTERNAL_FUNCTION("CREATE_DATE"),'yyyy-mm-dd')='20
13-06-02')

sys@ORCL> set autot off
sys@ORCL> create index idx_t_001 on t (to_char(create_date,'yyyy-mm-dd'));

Index created.

sys@ORCL> analyze index idx_t_001 validate structure;

Index analyzed.

sys@ORCL> select * from t where to_char(create_date,'yyyy-mm-dd')='2013-06-02';

no rows selected

sys@ORCL> set autot trace exp

第一种情况：小写

sys@ORCL> select * from t where to_char(create_date,'yyyy-mm-dd')='2013-06-02';

Execution Plan
----------------------------------------------------------
Plan hash value: 512271049

-----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 50 | 500 | 2 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| T | 50 | 500 | 2 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IDX_T_001 | 20 | | 1 (0)| 00:00:01 |
-----------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

2 - access(TO_CHAR(INTERNAL_FUNCTION("CREATE_DATE"),'yyyy-mm-dd')='2013-06-02'
)

第二种情况：首字母大写

sys@ORCL> select * from t where to_char(create_date,'yyyy-mm-Dd')='2013-06-02';

Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873

--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 50 | 500 | 5 (20)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T | 50 | 500 | 5 (20)| 00:00:01 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter(TO_CHAR(INTERNAL_FUNCTION("CREATE_DATE"),'yyyy-mm-Dd')='20
13-06-02')

第三种情况：大写

sys@ORCL> select * from t where to_char(create_date,'yyyy-mm-DD')='2013-06-02';

Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873

--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 50 | 500 | 5 (20)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T | 50 | 500 | 5 (20)| 00:00:01 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter(TO_CHAR(INTERNAL_FUNCTION("CREATE_DATE"),'yyyy-mm-DD')='20
13-06-02')