闪回表
oracle闪回表给予了DBA将一个或一组表快速恢复到过去的指定时间点并且不需要将数据库脱机。在大多数情况下闪回表与按时间点恢复操作相比消除了大量的操作。闪回表还原表时会自动维护与表相关的属性比如，当前索引，触发器和约束，并且不需要DBA找出和还原相关的属性。使用闪回表能将表回退到之前SCN或时间所对应的状态。
闪回表使用undo表空间中的信息来还原表。不需要从备份中还原任何数据，且在执行闪回表操作时数据库仍然可以使用。
使用闪回表的条件
使用闪回表有以下条件：
1.必须对表启用行移动。可以执行下面的语句来对表启用行移动：
alter table tablename enable row movement;
2.用户必须被授予了flashback any table的系统权限或者对特定的表有flashback对象权限
3.用户对于特定的表必须有select,insert,delete和alter权限
4.undo表空间中保留的undo信息足够能满足flashback table操作回退到所指定的时间点或SCN
下面测试闪回表
1.对表emp启用行移动
SQL> alter table emp enable row movement;
Table altered.
SQL> select * from emp;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- ------------ ---------- ---------- ----------
7369 SMITH CLERK 7902 17-DEC-80 800 20
7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30
7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30
7566 JONES MANAGER 7839 02-APR-81 2975 20
7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30
7698 BLAKE MANAGER 7839 01-MAY-81 2850 30
7782 CLARK MANAGER 7839 09-JUN-81 2450 10
7788 SCOTT ANALYST 7566 19-APR-87 3000 20
7839 KING PRESIDENT 17-NOV-81 5000 10
7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30
7876 ADAMS CLERK 7788 23-MAY-87 1100 20
7900 JAMES CLERK 7698 03-DEC-81 950 30
7902 FORD ANALYST 7566 03-DEC-81 3000 20
7934 MILLER CLERK 7782 23-JAN-82 1300 10
14 rows selected.
2.在删除表emp的记录之前记录一下时间或者SCN
SQL> select current_scn from v$database;
CURRENT_SCN
-----------
3077391
SQL> select sysdate from dual;
SYSDATE
-------------------
2015-02-02 20:50:39
3.删除表emp的记录
SQL> delete from emp; 14 rows deleted. SQL> commit; Commit complete. SQL> select * from emp; no rows selected
4.执行闪回表将表emp的内容回退到删除之前
使用flashback table tablename to scn的命令如下:
SQL> flashback table emp to scn 3077391;
Flashback complete.
SQL> select * from emp;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------
7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20
7499 ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30
7521 WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30
7566 JONES MANAGER 7839 1981-04-02 00:00:00 2975 20
7654 MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30
7698 BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30
7782 CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10
7788 SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20
7839 KING PRESIDENT 1981-11-17 00:00:00 5000 10
7844 TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30
7876 ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20
7900 JAMES CLERK 7698 1981-12-03 00:00:00 950 30
7902 FORD ANALYST 7566 1981-12-03 00:00:00 3000 20
7934 MILLER CLERK 7782 1982-01-23 00:00:00 1300 10
14 rows selected.
使用flashback table tablename to timestamp的命令如下:
SQL> flashback table emp to timestamp to_timestamp('2015-02-02 20:50:39','yyyy-mm-dd hh24:mi:ss');
Flashback complete.
SQL> select * from emp;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------
7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20
7499 ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30
7521 WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30
7566 JONES MANAGER 7839 1981-04-02 00:00:00 2975 20
7654 MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30
7698 BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30
7782 CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10
7788 SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20
7839 KING PRESIDENT 1981-11-17 00:00:00 5000 10
7844 TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30
7876 ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20
7900 JAMES CLERK 7698 1981-12-03 00:00:00 950 30
7902 FORD ANALYST 7566 1981-12-03 00:00:00 3000 20
7934 MILLER CLERK 7782 1982-01-23 00:00:00 1300 10
14 rows selected.
注意：timestamp到SCN之间的映射不总是精确的，当使用timestamp作为flashback table语句的时间点,闪回表的真实时间点与由to_timestamp所指定的时间点大约有三秒钟的差异。
默认情况下，在执行flashback table操作之前数据库对受影响的表禁用了触发器，将表闪回到所指定的时间点后，在对表执行操作之前启用触发器。如果想让表在执行flashback操作时启用触发器，那么可以在flashback table语句中加入enable triggers子句。
SQL> flashback table emp to timestamp to_timestamp('2015-02-02 20:50:39','yyyy-mm-dd hh24:mi:ss') enable triggers;
Flashback complete.
SQL> select * from emp;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------
7369 SMITH CLERK 7902 1980-12-17 00:00:00 800 20
7499 ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30
7521 WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30
7566 JONES MANAGER 7839 1981-04-02 00:00:00 2975 20
7654 MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30
7698 BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30
7782 CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10
7788 SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20
7839 KING PRESIDENT 1981-11-17 00:00:00 5000 10
7844 TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30
7876 ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20
7900 JAMES CLERK 7698 1981-12-03 00:00:00 950 30
7902 FORD ANALYST 7566 1981-12-03 00:00:00 3000 20
7934 MILLER CLERK 7782 1982-01-23 00:00:00 1300 10
14 rows selected.