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.
Answer: AD
答案解析：
参考：http://docs.oracle.com/cd/E11882_01/appdev.112/e41502/adfns_flashback.htm#ADFNS1006
Table 12-1 Oracle Flashback Version Query Row Data Pseudocolumns
| Pseudocolumn Name |
Description |
|---|
|
VERSIONS_STARTSCN
VERSIONS_STARTTIME
|
Starting System Change Number (SCN) or TIMESTAMP when the row version was created. This pseudocolumn identifies the time when the data first had the values reflected in the row version. Use this pseudocolumn to identify the past target time
for Oracle Flashback Table or Oracle Flashback Query.
If this pseudocolumn is NULL, then the row version was created before start.
|
|
VERSIONS_ENDSCN
VERSIONS_ENDTIME
|
SCN or TIMESTAMP when the row version expired.
If this pseudocolumn is NULL, then either the row version was current at the time of the query or the row corresponds to a DELETE operation.
|
|
VERSIONS_XID
|
Identifier of the transaction that created the row version.
|
|
VERSIONS_OPERATION
|
Operation performed by the transaction: I for insertion, D for deletion, or U for update. The version is that of the row that was inserted, deleted, or updated; that is, the row after anINSERT operation,
the row before a DELETE operation, or the row affected by an UPDATEoperation.
For user updates of an index key, Oracle Flashback Version Query might treat an UPDATEoperation as two operations, DELETE plus INSERT, represented as two version rows with a Dfollowed by an I VERSIONS_OPERATION.
|
Results are similar to:
XID START_SCN END_SCN O EMPNAME SALARY
---------------- ---------- ---------- - ---------------- ----------
09001100B2200000 10093466 I Tom 927
030002002B210000 10093459 D Mike 555
0800120096200000 10093375 10093459 I Mike 555
3 rows selected.
The results table rows are in descending chronological order. The third row corresponds to the version of the row in the table emp that was inserted in the table when the table was created. The second row corresponds to the
row in emp that the erroneous transaction deleted. The first row corresponds to the version of the row in emp that was reinserted with a new employee name.