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：/article/1629013.html

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.