OCP-1Z0-053-V12.02-63题

63.Which method would you use to undo the changes made by a particular transaction without affecting

the changes made by other transactions?

A. point-in-time recovery

B. execute the ROLLBACK command with transaction number

C. flashback the database to before the transaction was committed

D. determine all the necessary undo SQL statements from FLASHBACK_TRANSACTION_QUERY and

use them for recovery

Answer: D

答案解析：

参考：http://blog.csdn.net/rlhua/article/details/12404577

闪回查询：查询在特定时间点存在的所有数据。

使用闪回查询功能，可以执行截止到特定时间的查询。使用SELECT语句的AS OF子句，可以指定要查看其对应数据的时间戳。这在分析数据差异时非常有用。

注：TIMESTAMP和SCN是AS OF子句的有效选项。

UPDATE employees

SET salary =

(SELECT salary FROM employees

AS OF TIMESTAMP TO_TIMESTAMP

('2005-05-04 11:00:00', 'yyyy-mm-dd hh24:mi:ss')

WHERE employee_id = 200)

WHERE employee_id = 200

 

闪回查询：示例

如果最近错误地给某个雇员加了薪，则可重新更改薪金，其值由子查询返回的闪回值提供。

FLASHBACK_TRANSACTION_QUERY displays information about all flashback transaction queries in the database. The database must have at least minimal supplemental logging enabled to avoid unpredictable behavior.