反向索引與模糊查詢

安佰勝發表於2011-05-06

反向索引與模糊查詢
---------------------

版本

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Prod
PL/SQL Release 10.2.0.4.0 - Production
CORE 10.2.0.4.0 Production
TNS for 32-bit Windows: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production

測試資料
SQL> conn an/an
已連線。

SQL> create table atest(id int,name varchar2(100));
表已建立。

SQL> insert into atest select 1,'anbaisheng' from dual;
已建立 1 行。

SQL> insert into atest select 2,'xiangxiang' from dual;
已建立 1 行。

SQL> insert into atest select 3,'baby' from dual;
已建立 1 行。

SQL> commit;
提交完成。

SQL> select * from atest;
        ID NAME
---------- --------------------
         1 anbaisheng
         2 xiangxiang
         3 baby

建立正續索引
SQL> create index ind_name on atest(name);

索引已建立。

SQL> set autotrace on
SQL> select * from atest where name like 'a%';

        ID NAME
---------- --------------------
         1 anbaisheng

--------------------------------------------------------------------------------
| Id | Operation                   | Name     | Rows | Bytes | Cost (%CPU)| Ti
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |          |     1 |    65 |     2   (0)| 00
|   1 | TABLE ACCESS BY INDEX ROWID| ATEST    |     1 |    65 |     2   (0)| 00
|* 2 |   INDEX RANGE SCAN          | IND_NAME |     1 |       |     1   (0)| 00
--------------------------------------------------------------------------------

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

   2 - access("NAME" LIKE 'a%')
       filter("NAME" LIKE 'a%')

SQL> select * from atest where name like '%y';

        ID NAME
---------- --------------------
         3 baby

---------------------------------------------------------------------------
| Id | Operation         | Name | Rows | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT |       |     1 |    65 |     3   (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| ATEST |     1 |    65 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------

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

   1 - filter("NAME" LIKE '%y')

正向索引後模糊查詢有效，前模糊無效

建立反向索引
SQL> drop index ind_name;

索引已刪除。

SQL> create index ind_name on atest reverse(name);

索引已建立。

SQL> select * from atest where name like '%y';

        ID NAME
---------- --------------------
         3 baby

SQL> select * from atest where name like reverse ('%y');

未選定行

--------------------------------------------------------------------------------
| Id | Operation                   | Name     | Rows | Bytes | Cost (%CPU)| Ti
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |          |     1 |    65 |     0   (0)| 00
|   1 | TABLE ACCESS BY INDEX ROWID| ATEST    |     1 |    65 |     0   (0)| 00
|* 2 |   INDEX RANGE SCAN          | IND_NAME |     1 |       |     0   (0)| 00
--------------------------------------------------------------------------------

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

   2 - access("NAME" LIKE 'y%')
       filter("NAME" LIKE 'y%')

就算建上反向索引，不使用reverse關鍵字前模糊也沒用，後模糊無效

聯合部分反向索引
這個conception裡都沒說，自己試了下，還成
SQL> create index ind_idname on atest (id ,reverse(name));

索引已建立。

SQL> select * from atest where id=1 and name like reverse ('%y');

未選定行

--------------------------------------------------------------------------------
| Id | Operation                   | Name     | Rows | Bytes | Cost (%CPU)| Ti
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |          |     1 |    65 |     0   (0)| 00
|* 1 | TABLE ACCESS BY INDEX ROWID| ATEST    |     1 |    65 |     0   (0)| 00
|* 2 |   INDEX RANGE SCAN          | IND_NAME |     1 |       |     0   (0)| 00
--------------------------------------------------------------------------------

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

   1 - filter("ID"=1)
   2 - access("NAME" LIKE 'y%')
       filter("NAME" LIKE 'y%')

SQL> select * from atest where id=1 and name like '%y';

未選定行

--------------------------------------------------------------------------------
| Id | Operation                   | Name       | Rows | Bytes | Cost (%CPU)|
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |            |     1 |    65 |     2   (0)|
|* 1 | TABLE ACCESS BY INDEX ROWID| ATEST      |     1 |    65 |     2   (0)|
|* 2 |   INDEX RANGE SCAN          | IND_IDNAME |     1 |       |     1   (0)|
--------------------------------------------------------------------------------

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

   1 - filter("NAME" LIKE '%y')
   2 - access("ID"=1)

就算是聯合索引，不使用reverse的話意義也不大

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/13177610/viewspace-694601/，如需轉載，請註明出處，否則將追究法律責任。

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