178.All the database users are presently connected to the database instance and working. The HR user

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本文探讨了在数据库中执行UPDATE和DELETE操作但未提交时，这些更改对其他会话的可见性。根据读一致性原则，仅执行命令的会话能看到更改。

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178.All the database users are presently connected to the database instance and working. The HR user
has opened three database sessions and executed the following command in one of his sessions:
SQL> UPDATE persons SET ccode='U031' WHERE ccode='U029';
123 rows updated.
SQL> DELETE FROM persons WHERE exp='Y';
3 rows deleted.
The SYS user opens a new session after HR executed the above commands. Which sessions can see
the effect of the UPDATE and DELETE commands?
A.all sessions of the HR user only
B.all sessions of the HR user and the SYS user
C.the session of the HR user that executed the commands
D.all the sessions for which the database users have access privilege to the PERSONS table
答案：C
解析:这个其实就是undo的作用，读一致性，因为没有提交所以，其他会话所看到的记录还是旧的，只有自己才能看到效果