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SQL*Plus: Release 10.2.0.1.0 - Production on 星期五 3月 19 14:06:01 2010

Copyright (c) 1982, 2005, Oracle. All rights reserved.


连接到:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options

SQL> show parameter optimizer_mode

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
optimizer_mode string ALL_ROWS

SQL> alter session set optimizer_mode=rule;

会话已更改。

SQL> show parameter optimizer_mode

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
optimizer_mode string RULE

SQL> set autotrace on

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE 10.2.0.1.0 Production
TNS for 32-bit Windows: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production


执行计划
----------------------------------------------------------
Plan hash value: 1078166315

--------------------------------------
| Id | Operation | Name |
--------------------------------------
| 0 | SELECT STATEMENT | |
|* 1 | FIXED TABLE FULL| X$VERSION |
--------------------------------------

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

   1 - filter("INST_ID"=USERENV('INSTANCE'))

Note
-----
   - rule based optimizer used (consider using cbo) --Oracle给出的提示


统计信息
----------------------------------------------------------
          8 recursive calls
          0 db block gets
          2 consistent gets
          0 physical reads
          0 redo size
        680 bytes sent via SQL*Net to client
        385 bytes received via SQL*Net from client
          2 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
          5 rows processed

SQL> alter session set optimizer_mode=chooose;

ERROR:
ORA-00096: 值 CHOOOSE 对参数 optimizer_mode 无效, 它必须来自 first_rows_1000,
first_rows_100, first_rows_10, first_rows_1, first_rows, all_rows, choose, rule之间

-->一次错误输入，得到了参数的选项值

SQL> alter session set optimizer_mode=choose;

会话已更改。

SQL> show parameter optimizer_mode

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
optimizer_mode string CHOOSE
SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE 10.2.0.1.0 Production
TNS for 32-bit Windows: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production


执行计划
----------------------------------------------------------
Plan hash value: 1078166315

--------------------------------------
| Id | Operation | Name |
--------------------------------------
| 0 | SELECT STATEMENT | |
|* 1 | FIXED TABLE FULL| X$VERSION |
--------------------------------------

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

   1 - filter("INST_ID"=USERENV('INSTANCE'))

Note
-----
   - rule based optimizer used (consider using cbo) --Oracle给出的提示


统计信息
--------------------------- -->