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深蓝的blog：http://blog.csdn.net/huangyanlong/article/details/39935157
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实验项目：将undo表空间扩大，然后缩小
SQL> select name,bytes/1024/1024 M from v$datafile;
--查询undo表空间，当前为230m
NAME M
-------------------------------------------------- ----------
/u01/app/oracle/oradata/xcky/system01.dbf 760
/u01/app/oracle/oradata/xcky/sysaux01.dbf 550
/u01/app/oracle/oradata/xcky/undotbs01.dbf 230
/u01/app/oracle/oradata/xcky/users01.dbf 1518.75
/u01/app/oracle/oradata/xcky/example01.dbf 330
（1）、扩展undo表空间
思路：创建一个更大的undo表空间，让后将原undo空间替换
SQL> create undo tablespace undotbs02 datafile '/u01/app/oracle/oradata/xcky/undotbs02.dbf' size 500m reuse autoextend on;
Tablespace created.
SQL> alter system set undo_tablespace=undotbs02;
System altered.
SQL> select name,bytes/1024/1024 M from v$datafile;
--查询会发现，新扩展的undo表空间
NAME M
-------------------------------------------------- ----------
/u01/app/oracle/oradata/xcky/system01.dbf 760
/u01/app/oracle/oradata/xcky/sysaux01.dbf 550
/u01/app/oracle/oradata/xcky/undotbs01.dbf 230
/u01/app/oracle/oradata/xcky/users01.dbf 1518.75
/u01/app/oracle/oradata/xcky/example01.dbf 330
/u01/app/oracle/oradata/xcky/undotbs02.dbf 500
SQL> select tablespace_name,sum(bytes)/1024/1024 mb from dba_free_space group by tablespace_name;
--查找出之前undo表空间的名字
TABLESPACE_NAME MB
------------------------------ ----------
BULLETIN_INFO 499
INDEX_EIS 19
SYSAUX 33
UNDOTBS1 204.375
TBS_XZXT_PHOTO 19
TBS_XZXT_SYSTEM 19
VIEW_LOG 99
UNDOTBS02 497.75
......
SQL> drop tablespace UNDOTBS1 including contents and datafiles;
--删除undo表空间
Tablespace dropped.
SQL> select tablespace_name,sum(bytes)/1024/1024 mb from dba_free_space group by tablespace_name;
--再次查看undo表空间已经为新扩展的undo表空间了
TABLESPACE_NAME MB
------------------------------ ----------
BULLETIN_INFO 499
INDEX_EIS 19
SYSAUX 33
VIEW_LOG 99
UNDOTBS02 497.75
（2）、缩小undo表空间
思路：有了之前扩展undo表空间的方法，接下来缩小表空间便会变得简单了。原理一样，创建一个小的undo表空间，然后把大的undo表空间删除即可。
SQL> create undo tablespace UNDOTBS1 datafile '/u01/app/oracle/oradata/xcky/undotbs01.dbf' size 250m reuse autoextend on;
--创建一个小的undo表空间
Tablespace created.
SQL> alter system set UNDO_TABLESPACE=UNDOTBS1;
--改变undo表空间为UNDOTBS1
System altered.
SQL> select tablespace_name,sum(bytes)/1024/1024 mb from dba_free_space group by tablespace_name;
--再次查询，新建的undo表空间已经显示
TABLESPACE_NAME MB
------------------------------ ----------
BULLETIN_INFO 499
INDEX_EIS 19
SYSAUX 33
UNDOTBS1 247.75
UNDOTBS02 497.75
SQL> drop tablespace UNDOTBS02 including contents and datafiles;
--删除大的undo表空间
Tablespace dropped.
SQL> select tablespace_name,sum(bytes)/1024/1024 mb from dba_free_space group by tablespace_name;
--查看表空间情况，已经完成了缩小undo表空间
TABLESPACE_NAME MB
------------------------------ ----------
BULLETIN_INFO 499
INDEX_EIS 19
SYSAUX 33
UNDOTBS1 247.75
结合以上实验过程，编写脚本，可以减轻日后的工作量，有了上面的基础，看懂下面的语句应该是so easy了吧，O(∩_∩)O哈哈~
指令如下：
脚本实现：
[root@xckydb soft]# vi query_undo.sql
--编写