Research on the Oracle 11g

A test regarding vitual index:

C:/Users/henry>sqlplus / as sysdba

SQL*Plus: Release 11.1.0.6.0 - Production on 星期四 7月 24 14:57:58 2008

Copyright (c) 1982, 2007, Oracle. All rights reserved.

连接到:
Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> select * from v$version;

BANNER
--------------------------------------------------------------------------------

Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
PL/SQL Release 11.1.0.6.0 - Production
CORE 11.1.0.6.0 Production
TNS for 32-bit Windows: Version 11.1.0.6.0 - Production
NLSRTL Version 11.1.0.6.0 - Production

SQL> create table test(id int,name varchar2(30));

表已创建。

SQL> insert into test select rownum,object_name from all_objects
2 /

已创建68193行。

SQL>
SQL>
SQL> commit;

提交完成。

SQL> create unique index ix_test on test(id) nosegment;

索引已创建。

SQL>
SQL> explain plan for select * from test where id=1;

已解释。

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

Plan hash value: 1357081020

--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 30 | 91 (2)| 00:00:02 |
|* 1 | TABLE ACCESS FULL| TEST | 1 | 30 | 91 (2)| 00:00:02 |
--------------------------------------------------------------------------

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

1 - filter("ID"=1)

Note
-----
- dynamic sampling used for this statement

已选择17行。

SQL> analyze table test compute statistics;

表已分析。

SQL> explain plan for select * from test where id=1;

已解释。

SQL> explain plan for select * from test where id=1;

已解释。

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

Plan hash value: 1357081020

--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 28 | 91 (2)| 00:00:02 |
|* 1 | TABLE ACCESS FULL| TEST | 1 | 28 | 91 (2)| 00:00:02 |
--------------------------------------------------------------------------

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

1 - filter("ID"=1)

已选择13行。

SQL> alter session set "_use_nosegment_indexes"=true;

会话已更改。

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

Plan hash value: 1357081020

--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 28 | 91 (2)| 00:00:02 |
|* 1 | TABLE ACCESS FULL| TEST | 1 | 28 | 91 (2)| 00:00:02 |
--------------------------------------------------------------------------

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

1 - filter("ID"=1)

已选择13行。

SQL> explain plan for select * from test where id=1;

已解释。

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

Plan hash value: 166686173

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

-------

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

e |

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

-------

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 1 | 28 | 2 (0)| 00:

00:01 |

| 1 | TABLE ACCESS BY INDEX ROWID| TEST | 1 | 28 | 2 (0)| 00:

00:01 |

|* 2 | INDEX UNIQUE SCAN | IX_TEST | 1 | | 1 (0)| 00:

00:01 |

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

-------

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

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

2 - access("ID"=1)

已选择14行。

SQL>

This is maybe very helpful for the tuning SQL.