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？（）

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？（）

A.The extents in undo tablespace retain data until the next full database backup.
B.The extents containing committed data in the undo tablespace are never overwritten.
C.The extents which no longer contain uncommitted data in the undo tablespace are not overwritten for at least15 minutes.
D.The extents containing committed data in the undo tablespace are not overwritten until the instance  is shut down.

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？（）

A.increase the size of redo log files
B.increase the size of the undo tablespace
C.increase the size of the Database Buffer Cache
D.increase the size of the default temporary tablespace
E.enable the retention guarantee for the undo tablespace

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？（）

A.LOCK TABLE emp IN SHARE MODE;
B.LOCK TABLE emp IN EXCLUSIVE MODE;
C.DELETE FROM emp WHERE job=’MANAGER’;
D.INSERT INTO emp（empno，ename） VALUES （1289，’Dick’）;
E.SELECT job FROM emp WHERE job=’CLERK’ FOR UPDATE OF empno;

多项选择题WhichtwoarevalidlockinglevelsthatareusedbytransactionsinanOracledatabase？（）

A.row level
B.block level
C.object level
D.schema level
E.database level

单项选择题The ST_INFO master table has millions of rows that are updated very rarely. It has a STATE_CODE column that contains the value for 25 states. The table is frequently queried on the STATE_CODE column.  Which type of index would you suggest to improve the query performance？（）

A.B­tree
B.bitmap
C.reverse key
D.function based