Oracle的分析函数ROW_NUMBER、DENSE_RANK、RANKOracle的分析函数ROW_NUMBER、DENSE_RANK、RANK

共同点：这三个分析函数都可以在各个分组内从1开始排序。

区别：ROW_NUMBER()是没有重复值的，可以利用它实现分页显示。

DENSE_RANK()是连续排序，有两个第二名时仍然跟着第三名。

RANK()是跳跃排序，有两个第二名时接下来就是第四名（同样是在各个分组内）。

SELECT * FROM (

SELECT deptno, ename, sal, ROW_NUMBER()

OVER (

PARTITION BY deptno ORDER BY sal DESC

) Top3 FROM emp

)

WHERE Top3 <= 3

/

DEPTNO ENAME SAL TOP3

---------- ---------- ---------- ----------

10 KING 5000 1

10 CLARK 2450 2

10 MILLER 1300 3

20 SCOTT 3000 1

20 FORD 3000 2

20 JONES 2975 3

30 BLAKE 2850 1

30 ALLEN 1600 2

30 TURNER 1500 3

9 rows selected.

SELECT * FROM (

SELECT deptno, ename, sal, DENSE_RANK()

OVER (

PARTITION BY deptno ORDER BY sal DESC

) TopN FROM emp

)

WHERE TopN <= 3

ORDER BY deptno, sal DESC

/

DEPTNO ENAME SAL TOPN

---------- ---------- ---------- ----------

10 KING 5000 1

10 CLARK 2450 2

10 MILLER 1300 3

20 SCOTT 3000 1 <--- !

20 FORD 3000 1 <--- !

20 JONES 2975 2

20 ADAMS 1100 3

30 BLAKE 2850 1

30 ALLEN 1600 2

30 TURNER 1500 3

10 rows selected.

SELECT * FROM (

SELECT deptno, ename, sal, RANK()

OVER (

PARTITION BY deptno ORDER BY sal DESC

) TopN FROM emp

)

WHERE TopN <= 3

ORDER BY deptno, sal DESC

/

DEPTNO ENAME SAL TOPN

---------- ---------- ---------- ----------

10 KING 5000 1

10 CLARK 2450 2

10 MILLER 1300 3

20 SCOTT 3000 1 <--- !

20 FORD 3000 1 <--- !

20 JONES 2975 3

30 BLAKE 2850 1

30 ALLEN 1600 2

30 TURNER 1500 3

9 rows selected