闪回查询（SELECT AS OF）

使用Flashback Query的场景包括如下：

摘自官档

• Recovering lost data or undoing incorrect, committed changes.

  For example, if you mistakenly delete or update rows, and then commit them, you can immediately undo the mistake.

• Comparing current data with the corresponding data at an earlier time.

  For example, you can run a daily report that shows the change in data from yesterday. You can compare individual rows of table data or find intersections or unions of sets of rows.

• Checking the state of transactional data at a particular time.

  For example, you can verify the account balance of a certain day.

• Simplifying application design by removing the need to store some kinds of temporal data.

  Oracle Flashback Query lets you retrieve past data directly from the database.

• Applying packaged applications, such as report generation tools, to past data.

• Providing self-service error correction for an application, thereby enabling users to undo and correct their errors.

• 需要授予 FLASHBACK ANY TABLE 权限

假设表personnel在早上4点30的时候发现Smith的记录被删，DBA确定在前天晚上7点30的时候数据是准确的，于是我们可以使用Flashback Query技术找回丢失的数据

查纪录

SELECT * 

  FROM personnel

  AS OF TIMESTAMP

  TO_TIMESTAMP('2012-03-21 07:30:00', 'YYYY-MM-DD HH:MI:SS')

WHERE UPPER(last_name) = 'SMITH';

使用闪回查询恢复数据

INSERT INTO personnel 

 (

  SELECT * 

    FROM personnel

    AS OF TIMESTAMP

    TO_TIMESTAMP('2012-03-21 07:30:00', 'YYYY-MM-DD HH:MI:SS')

   WHERE UPPER(last_name) = 'SMITH'

 );

创建过去表的一个视图

CREATE VIEW hour_ago AS

  SELECT * FROM employees

    AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '60' MINUTE);

• 可以在自连接中使用AS OF子句，或者INTERSECT 和 MINUS提取或者比较两个不同时间点的数据

也可以使用下面的方法恢复丢失的数据

INSERT INTO employees

    (SELECT * FROM employees

     AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '60' MINUTE)

    MINUS SELECT * FROM employees;

场景

CREATE TABLE flashback_query_test (

  id  NUMBER(10)

);



SELECT current_scn, TO_CHAR(SYSTIMESTAMP, 'YYYY-MM-DD HH24:MI:SS') FROM v$database;



CURRENT_SCN TO_CHAR(SYSTIMESTAM

----------- -------------------

     722452 2004-03-29 13:34:12



INSERT INTO flashback_query_test (id) VALUES (1);

COMMIT;



SELECT COUNT(*) FROM flashback_query_test;



  COUNT(*)

----------

         1



SELECT COUNT(*)

FROM   flashback_query_test AS OF TIMESTAMP TO_TIMESTAMP('2004-03-29 13:34:12', 'YYYY-MM-DD HH24:MI:SS');



  COUNT(*)

----------

         0



SELECT COUNT(*)

FROM   flashback_query_test AS OF SCN 722452;



  COUNT(*)

----------

         0

使用DBMS_FLASHBACK进程闪回查询

This can as well been done with SCN using ENABLE_AT_SYSTEM_CHANGE_NUMBER procedure or timestamp usingENABLE_AT_TIME procedure:

     
       

      
        
SQL> SELECT current_scn, SCN_TO_TIMESTAMP(current_scn),TO_CHAR(SYSDATE,'dd-mon-yyyy hh24:mi:ss') AS current_time FROM v$database;
      
        

      
        
CURRENT_SCN SCN_TO_TIMESTAMP(CURRENT_SCN) CURRENT_TIME
      
        
----------- --------------------------------------------------------------------------- -----------------------------
      
        
 28954179 15-AUG-11 11.03.48.000000000 AM 15-aug-2011 11:03:48
      
        

      
        
SQL> EXEC dbms_flashback.enable_at_system_change_number(28954179);
      
        

      
        
PL/SQL PROCEDURE successfully completed.
      
        

      
        
SQL> SELECT * FROM test1;
      
        

      
        
 ID DESCR
      
        
---------- ------------------------------
      
        
 1 One
      
        
 2 Two
      
        
 3 Three
      
        

      
        
SQL> EXEC dbms_flashback.disable;
      
        

      
        
PL/SQL PROCEDURE successfully completed.
      
        

      
        
SQL> SELECT * FROM test1;
      
        

      
        
 ID DESCR
      
        
---------- ------------------------------
      
        
 1 TEMPORARY
      
        
 2 TEMPORARY
      
        
 3 TEMPORARY
     
       

最后,闪回表到过去，（效果和上面的insert into as select一样）

     
       

      
        
SQL> flashback TABLE test1 TO scn 28954179;
      
        

      
        
Flashback complete.
      
        

      
        
SQL> SELECT * FROM test1;
      
        

      
        
 ID DESCR
      
        
---------- ------------------------------
      
        
 1 One
      
        
 2 Two
      
        
 3 Three
     
       

来自为知笔记(Wiz)