1.闪回查询

原理：用户恢复删除的数据，利用的是undo表空间的数据，闪回查询过去的某一个时间点或SCN的数据信息。

SYS@PROD> conn scott/tiger
SCOTT@PROD> create table t_fb_query1 as select * from dept;
SCOTT@PROD> select * from t_fb_query1;

    DEPTNO DNAME          LOC
---------- -------------- -------------
        10 ACCOUNTING     NEW YORK
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON
SCOTT@PROD> set time on
14:30:49 SCOTT@PROD> select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual;
##也可以更改当前会话的时间格式：
alter session set nls_date_format='yyyy-mm-dd hh24:miss';
select sysdate from dual;
2021-09-11 10:02:15
##查询当前SCN
14:31:58 SYS@PROD> select current_scn from v$database;

CURRENT_SCN
-----------
    1070729
    
模拟删除10号部门的数据
14:33:25 SCOTT@PROD> delete t_fb_query1 where deptno=10;
14:33:53 SCOTT@PROD> select * from t_fb_query1;

    DEPTNO DNAME          LOC
---------- -------------- -------------
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON


语法：select * from 表名 as of  timestamp/SCN;

select * from t_fb_query1 
as of timestamp to_timestamp('2021-09-11 10:02:15','yyyy-mm-dd hh24:mi:ss');
   DEPTNO DNAME          LOC
---------- -------------- -------------
        10 ACCOUNTING     NEW YORK
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON
   
 ##利用SCN查询   
14:35:31 SCOTT@PROD> select * from t_fb_query1 as of SCN  1070729;

    DEPTNO DNAME          LOC
---------- -------------- -------------
        10 ACCOUNTING     NEW YORK
        20 RESEARCH       DALLAS
        30 SALES          CHICAGO
        40 OPERATIONS     BOSTON
        
##插入闪回的数据  
insert into scott.t_fb_query1
select * from scott.t_fb_query1 
as of timestamp to_timestamp('2021-09-11 10:02:15','yyyy-mm-dd hh24:mi:ss')
minus
select * from scott.t_fb_query1;

2.闪回表

原理：利用的是Undo表空间的undo数据，闪回表到某个时间点或某个SCN
##连接SCOTT用户创建业务表：
conn scott/tiger
create table fb_1 (id number);
insert into fb_1 values(10);
commit;


alter session set nls_date_format='yyyy-mm-dd hh24:mi:ss';
select sysdate from dual;


##查看此时的时间或者SCN:
时间：
select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual;
2021-09-11 10:17:27
SCN:conn / as sysdba 
select current_scn from v$database;
CURRENT_SCN
-----------
     1071438

##执行数据删除操作：
delete from scott.fb_1;
commit;

##闪回表到数据删除之前

开启被闪回表的行迁移：
14:42:45 SYS@PROD> alter table scott.fb_1 enable row movement;
 
 闪回查询确认数据：
select  * from scott.fb_1 as of scn 1071438;

执行闪回,可以执行多次闪回操作：
flashback table scott.fb_1 to scn  1071438;

或者
flashback table scott.fb_1 
to timestamp to_timestamp('2021-09-11 10:17:27','yyyy-mm-dd hh24:mi:ss');

验证数据：
SYS@PROD> select * from scott.fb_1;
        ID
----------
        10
##关闭行迁移
SYS@PROD> alter table scott.fb_1 disable row movement;