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The user SCOTT executes the following command successfully to increase the salary values in one of his sessions：  SQL> UPDATE emp SET sal=sal*1.15 WHERE deptno=20；  Before SCOTT ends the transaction， user HR who has the privileges on EMP table executes a query to fetch the salary details but finds the old salary values instead of the increased values. Why does HR still see the old data？（）
A:because of redo data from redo log file
B:because of data from database buffer cache
C:because of data from a temporary tablespace
D:because of undo data from the undo tablespace

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出自：Oracle认证

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