rowid和rownum有什么不同？区别在哪里？

A.limit

B.rownum

C.rowcount

D.rowid

A.LEVEL

B.ROW_NUMBER()

C.ROWNUM

D.COLUMN

E.ROWID

_NAME VARCHAR2(30)COURSE_ID VARCHAR2(10) NOT NULLMARKS NUMBERSTART_DATE DATEFINISH_DATE DATEYou 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‘;

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