（616）The EMP table has some discrepancy in data entry with a particular employee ID.

You execute the query as shown in the Exhibit to retrieve all versions of the row that exist between two SCNs.View the Exhibit.

Which two statements about the results of the query shown in the Exhibit are correct?(Choose two.)

Exhibit:

A. The LAST_SCN value in the first row is NULL,which means that the versions of the row still exist at SCN 6636300.

B. The LAST_SCN value in the second row in NULL,which means that the version of the row still exists at SCN 6636300.

C. The LAST_SCN value in the third row is 6636280,which means that the version of row exists above SCN 6636280.

D. The LAST_SCN value in the second row is NULL,which means that the version of the row no longer exists because it was deleted.

答案：（A、D）

解析：

闪回版本查询用来找到在两个时间点（SCN）之前表到底发生了什么事情。

A，因为第一行的first_scn是做insert操作，而last_scn是空的，意味着该行还存在

D，从图上看出第三行first_scn=6636252的时候insert了一行，ename等于”Jones”，但是其存在的生命周期在 last_scn=6636280 就结束了，

为什么结束了，看第二行scn 6636280做了一个delete操作

ITPub博客

Oracle 11G OCP 1Z0-053 616