You need to change the definition of an existing table. The COMMERCIALS table needs its DESCRIPTION column changed to hold varying length characters up to 2000 bytes. The column can currently hold 1000 bytes per value. The table contains 20000 rows.
Which statement is valid?（）

单项选择题What does the TRUNCATE statement do?（）

A. Removes the table
B. Removes all rows from a table
C. Shortens the table to 10 rows
D. Removes all columns from a table
E. Removes foreign keys from a table

单项选择题Which is an SQL*Plus command?（）

A. INSERT
B. UPDATE
C. SELECT
D. DESCRIBE
E. DELETE
F. RENAME

单项选择题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 mark 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 mark;
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 mark DESC;
D. SELECT student_id, marks, ROWNUM "Rank" FROM (SELECT student_id, marks FROM students WHERE (finish_date BETWEEN '01-JAN-99 AND '31-DEC-99' AND course_id = 'INT_SQL' ORDER BY marks DESC) WHERE ROWNUM <= 10;
E. SELECT student id, marks, ROWNUM "Rank" FROM (SELECT student_id, marks FROM students ORDER BY marks) WHERE ROWNUM <= 10 AND finish date BETWEEN '01-JAN-99' AND '31-DEC-99' AND course _ id 'INT_SQL';

单项选择题Which SELECT statement should you use to extract the year from the system date and display it in the format 1998 ?（）

A. SELECT TO_CHAR(SYSDATE,'yyyy')   FROM dual;
B. SELECT TO_DATE(SYSDATE,'yyyy')   FROM dual;
C. SELECT DECODE(SUBSTR(SYSDATE, 8), 'YYYY')   FROM dual;
D. SELECT DECODE(SUBSTR(SYSDATE, 8), 'year')   FROM dual;
E. SELECT TO_CHAR(SUBSTR(SYSDATE, 8,2),'yyyy')   FROM dual;

单项选择题Which statement correctly describes SQL and SQL*Plus?（）

A. Both SQL and /SQL*plus allow manipulation of values in the database.
B. /SQL* Plus recognizes SQL satement and sends them to the server; SQL is the Oracle proprietary interface for executing SQL statements.
C. /SQL* Plus language for communicating with the Oracle server to access data; SQL recognizes SQL statements and sends them to the server.
D. /SQL manipulates data and table definition in the database; /SQL* Plus does not allow manipulation of values in the database.