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HomeDatabaseMysql TutorialORACLE 回收站当前状态查询整理

回收站(Recycle Bin)从原理上来说就是一个数据字典表,放置用户删除(drop)掉的数据库对象信息,接下来详细介绍下ORACLE 回收站方方面面感兴趣的你可以参考下哈

回收站(Recycle Bin)从原理上来说就是一个数据字典表,放置用户删除(drop)掉的数据库对象信息。用户进行删除操作的对象并没有被数据库删除,仍然会占用空间。除非是由于用户手工进行Purge或者因为存储空间不够而被数据库清掉。

在Oracle 10g数据库中,引入了一个回收站(Recycle Bin)的数据库对象。
回收站,顾名思义,它就是存储被删掉的东西。从原理上来说就是一个数据字典表,放置用户删除(drop)掉的数据库对象信息。用户进行删除操作的对象并没有被数据库删除,仍然会占用空间。除非是由于用户手工进行Purge或者因为存储空间不够而被数据库清掉。数据库有了这样的功能,能够减少很多不必要的麻烦。
如果一个表被删除,那么与该表有关联的对象,例如索引、约束和其他依赖对象都会在前面加bin$$这个前缀。

启动和关闭
你可以使用下面的查询语句来查看回收站的当前状态:

1.SELECT Value FROM V$parameter WHERE Name = 'recyclebin';
如果返回值为“on”表明回收站是启动的,“off”表明是关闭的。
当然,你可以启动或者关闭回收站里的每个会话(session)和系统(system),代码如下:
代码如下:
ALTER SYSTEM SET recyclebin = ON;
ALTER SESSION SET recyclebin = ON;
ALTER SYSTEM SET recyclebin = OFF;
ALTER SESSION SET recyclebin = OFF;

获取回收站里的内容
你可以使用下面的任意一个语句来获得回收站中的对象:
代码如下:
SELECT * FROM RECYCLEBIN;
SELECT * FROM USER_RECYCLEBIN;
SELECT * FROM DBA_RECYCLEBIN;

还原
可以使用如下语法来还原被删除的对象:
代码如下:
FLASHBACK TABLE > TO BEFORE DROP RENAME TO >;

备注:这里的RENAME是给删除的对象进行重新命名,是一个可选命令。
清空回收站
这里的清空包含两种情况,第一你可以有条件的清空;第二是全部清空。我们先来看看有条件的清空该如何做:
a.清空一个特定的表:
代码如下:
PURGE TABLE >;

b.清空一个特定的索引:
代码如下:
PURGE INDEX >;

c.清空与该表空间有关联的对象:
代码如下:
PURGE TABLESPACE>;

d.清空一个特定用户的表空间对象:
代码如下:
PURGE TABLESPACE> USER >;

e.清空回收站:
代码如下:
PURGE RECYCLEBIN;

f.当一个表被删除(drop)时就直接从回收站中清空
代码如下:
DROP TABLE > PURGE;

Demo
1.启动回收站功能
代码如下:
ALTER SYSTEM SET recyclebin = ON;

2.创建一个DEMO_RECYCLEBIN表
代码如下:
CREATE TABLE DEMO_RECYCLEBIN (COL1 NUMBER);

3.向DEMO_RECYCLEBIN表中插入一条数据
代码如下:
INSERT INTO DEMO_RECYCLEBIN (COL1) VALUES (1); COMMIT;

4.删除(Drop)DEMO_RECYCLEBIN表
代码如下:
DROP TABLE DEMO_RECYCLEBIN;

5.查询
代码如下:
SELECT * FROM USER_RECYCLEBIN;

结果:
6.从回收站中还原DEMO_RECYCLEBIN表
代码如下:
FLASHBACK TABLE DEMO_RECYCLEBIN TO BEFORE DROP;

7.还原后查询
代码如下:
SELECT * FROM DEMO_RECYCLEBIN;

查询结果和删除前是一致的。
8.删除表,并且将其从回收站中清空
代码如下:
DROP TABLE DEMO_RECYCLEBIN PURGE;
Statement
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