Oracle row_number 
       dense_rank
       rank

看結果集的倒數 2 3 行資料就明白了.


[email protected]>select * from emp;

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
      7369 SMITH      CLERK           7902 17-DEC-80        800                    20
      7499 ALLEN      SALESMAN        7698 20-FEB-81       1600        300         30
      7521 WARD       SALESMAN        7698 22-FEB-81       1250        500         30
      7566 JONES      MANAGER         7839 02-APR-81       2975                    20
      7654 MARTIN     SALESMAN        7698 28-SEP-81       1250       1400         30
      7698 BLAKE      MANAGER         7839 01-MAY-81       2850                    30
      7782 CLARK      MANAGER         7839 09-JUN-81       2450                    10
      7839 KING       PRESIDENT            17-NOV-81       5000                    10
      7844 TURNER     SALESMAN        7698 08-SEP-81       1500          0         30
      7876 ADAMS      CLERK           7788 23-MAY-87       1100                    20
      7900 JAMES      CLERK           7698 03-DEC-81        950                    30
      7902 FORD       ANALYST         7566 03-DEC-81       3000                    20
      7934 MILLER     CLERK           7782 23-JAN-82       1300                    10




 
[email protected]>select ename,deptno,sal,row_number() over(partition by deptno order by sal desc) rn from emp;

ENAME          DEPTNO        SAL         RN
---------- ---------- ---------- ----------
KING               10       5000          1
CLARK              10       2450          2
MILLER             10       1300          3
FORD               20       3000          1
JONES              20       2975          2
ADAMS              20       1100          3
SMITH              20        800          4
BLAKE              30       2850          1
ALLEN              30       1600          2
TURNER             30       1500          3
MARTIN             30       1250          4
WARD               30       1250          5
JAMES              30        950          6



 
[email protected]>select ename,deptno,sal,dense_rank() over(partition by deptno order by sal desc) rn from emp;

ENAME          DEPTNO        SAL         RN
---------- ---------- ---------- ----------
KING               10       5000          1
CLARK              10       2450          2
MILLER             10       1300          3
FORD               20       3000          1
JONES              20       2975          2
ADAMS              20       1100          3
SMITH              20        800          4
BLAKE              30       2850          1
ALLEN              30       1600          2
TURNER             30       1500          3
MARTIN             30       1250          4
WARD               30       1250          4
JAMES              30        950          5


 
[email protected]>select ename,deptno,sal,rank() over(partition by deptno order by sal desc) rn from emp;

ENAME          DEPTNO        SAL         RN
---------- ---------- ---------- ----------
KING               10       5000          1
CLARK              10       2450          2
MILLER             10       1300          3
FORD               20       3000          1
JONES              20       2975          2
ADAMS              20       1100          3
SMITH              20        800          4
BLAKE              30       2850          1
ALLEN              30       1600          2
TURNER             30       1500          3
MARTIN             30       1250          4
WARD               30       1250          4
JAMES              30        950          6