43.View the following SQL statements:
Transaction T1 INSERT INTO hr.regions VALUES (5,'Pole');COMMIT;
Transaction T2 UPDATE hr.regions SET region_name='Poles' WHERE region_id = 5; COMMIT;
Transaction T3 UPDATE hr.regions SET region_name='North and South Poles' WHERE region_id = 5;
You want to back out transaction T2. Which option would you use?
A. It is possible, but transaction T3 also backs out.
B. It is possible with the NOCASCADE_FORCE option.
C. It is possible with the NONCONFLICT_ONLY option.
D. It is not possible because it has conflicts with transaction T3.
Answer: B
答案解析：
参考：http://docs.oracle.com/cd/E11882_01/appdev.112/e41502/adfns_flashback.htm#ADFNS627
NOCASCADE_FORCE - The user forcibly backs out the given transactions without considering the dependent transactions. The RDBMS executes the UNDO SQL for
the given transactions in reverse order of their commit times. If no constraints break, and the result is satisfactory, the user can eitherCOMMIT the changes or else ROLL BACK.
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Backs out specified transactions, ignoring dependent transactions. Server runs undo SQL statements for specified transactions in reverse order of commit times. If no constraints break and you are satisfied with the result, you can commit the changes; otherwise, you can roll them back. |