多选题These are the details about V$FLASHBACK_DATABASE_STAT： SQL DESC v$FLASHBACK_DATABASE_STAT  Name                    Null？              Type  ------------- -------- --------------  BEGIN_TIME                               DATE  END_TIME                  

第1题：

第2题：

Examine the structure of the STUDENTS table: STUDENT_ID NUMBER NOT NULL, Primary Key STUDENT_NAME VARCHAR2(30) COURSE_ID VARCHAR2(10) NOT NULL MARKS NUMBER START_DATE DATE FINISH_DATE DATE You need to create a report of the 10 students who achieved the highest ranking in the course INT SQL and who completed the course in the year 1999. Which SQL statement accomplishes this task?（）

• A、SELECT student_ id, marks, ROWNUM "Rank" FROM students WHERE ROWNUM <= 10 AND finish_date BETWEEN '01-JAN-99' AND '31-DEC-99' AND course_id = 'INT_SQL' ORDER BY marks DESC;
• B、SELECT student_id, marks, ROWID "Rank" FROM students WHERE ROWID <= 10 AND finish_date BETWEEN '01-JAN-99' AND '31-DEC-99' AND course_id = 'INT_SQL' ORDER BY marks;
• C、SELECT student_id, marks, ROWNUM "Rank" FROM (SELECT student_id, marks FROM students WHERE ROWNUM <= 10 AND finish_date BETWEEN '01-JAN-99' AND '31-DEC-99' AND course_id = 'INT_SQL' ORDER BY marks DESC);
• D、SELECT student_id, marks, ROWNUM "Rank" FROM (SELECT student_id, marks FROM students ORDER BY marks DESC) WHERE ROWNUM <= 10 AND finish_date BETWEEN '01-JAN-99' AND '31-DEC-99' AND course _ id ='INT _ SQL';

第3题：

第4题：

On Friday at 11:30 am you decided to flash back the database because of a user error that occurred at 8:30 am. Which option must you use to check whether a flashback operation can recover the database to the specified time? （）

• A、Check the alert log file
• B、Query the V$FLASHBACK_DATABASE_LOG view
• C、Query the V$RECOVERY_FILE_DEST_SIZE view
• D、Query the V$FLASHBACK_DATABASE_STAT view
• E、Check the value assigned for the UNDO_RETENTION parameter

第5题：

Evaluate these two SQL statements: SELECT last_name, salary , hire_date FROM EMPLOYEES ORDER BY salary DESC; SELECT last_name, salary , hire_date FROM EMPLOYEES ORDER BY 2 DESC; What is true about them?（）

• A、The two statements produce identical results.
• B、The second statement returns a syntax error.
• C、There is no need to specify DESC because the results are sorted in descending order by default.
• D、The two statements can be made to produce identical results by adding a column alias for the salary column in the second SQL statement.

第6题：

第7题：

The EMPLOYEES table has these columns: LAST NAME VARCHAR2(35) SALARY NUMBER(8,2) HIRE_DATE DATE Management wants to add a default value to the SALARY column. You plan to alter the table by using this SQL statement: ALTER TABLE EMPLOYEES MODIFY ( SALARY DEFAULT 5000); What is true about your ALTER statement?（）

• A、Column definitions cannot be altered to add DEFAULT values.
• B、A change to the DEFAULT value affects only subsequent insertions to the table.
• C、Column definitions cannot be altered at add DEFAULT values for columns with a NUMBER data type.
• D、All the rows that have a NULL value for the SALARY column will be updated with the value 5000.

第8题：

第9题：

以下的PL/SQL声明哪个是正确的？（）

• A、v_id NUMBER(4);
• B、v_x, v_y, v_z VARCHAR2(10);
• C、v_birthdate DATE NOT NULL;
• D、v_in_stock BOOLEAN := 1;

第10题：

These are the details about V$FLASHBACK_DATABASE_STAT：  SQL> DESC V$FLASHBACK_DATABASE_STAT Name Null？ Type  ------------- -------- --------------  BEGIN_TIME DATE END_TIME DATE  FLASHBACK_DATA NUMBER  DB_DATA NUMBER REDO_DATA NUMBER  ESTIMATED_FLASHBACK_SIZE NUMBER  Which two statements regarding the V$FLASHBACK_DATABASE_STAT view are true？ （）

• A、BEGIN_TIME is the time at which Flashback logging is enabled.
• B、END_TIME is the time at which the query is executed on the view.
• C、REDO_DATA is the number of bytes of redo data written during the interval.
• D、This view contains information about flashback data pertaining to the last 24 hours.
• E、FLASHBACK_DATA is the amount of flashback data generated since the database was opened.