单项选择题
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
单项选择题 Your database is running under automatic undo management and the UNDO_RETENTION parameter is set to 900 sec. You executed the following command to enable retention guarantee： SQL> ALTER TABLESPACE undotbs1 RETENTION GUARANTEE What effect would this statement have on the database？（）
多项选择题 A user receives the following error while executing a query： ORA01555：snapshot too old Which two options can be the solutions to avoid such errors in future？（）
多项选择题 User SCOTT executes the following command on the EMP table but has not issued COMMIT， ROLLBACK，or any data definition language （DDL） command： SQL> SELECT job FROM emp 2 WHERE job=’CLERK’ FOR UPDATE OF empno SCOTT has opened another session to work with the database. Which three operations would wait when issued in SCOTT’s second session？（）