oracle row_number分析函数

oracle 分许函数 row_number(),返回一个整数值(>=1);

语法格式:

1.row_number() over (order by col_1[,col_2 ...])

作用:按照col_1[,col_2 ...]排序,返回排序后的结果集，

此用法有点像rownum,为每一行返回一个不相同的值：

select rownum,ename,job,
       row_number() over (order by rownum) row_number
from emp;
    ROWNUM ENAME      JOB       ROW_NUMBER
---------- ---------- --------- ----------
         1 SMITH      CLERK              1
         2 ALLEN      SALESMAN           2
         3 WARD       SALESMAN           3
         4 JONES      MANAGER            4
         5 MARTIN     SALESMAN           5
         6 BLAKE      MANAGER            6
         7 CLARK      MANAGER            7
         8 SCOTT      ANALYST            8
         9 KING       PRESIDENT          9
        10 TURNER     SALESMAN          10
        11 ADAMS      CLERK             11
        12 JAMES      CLERK             12
        13 FORD       ANALYST           13
        14 MILLER     CLERK             14

如果没有partition by子句, 结果集将是按照order by 指定的列进行排序；

with row_number_test as(
     select 22 a,'twenty two' b from dual union all
     select 1,'one' from dual union all
     select 13,'thirteen' from dual union all
     select 5,'five' from dual union all
     select 4,'four' from dual)
select a,b,
       row_number() over (order by b)
from row_number_test
order by a;

正如我们所期待的,row_number()返回按照b列排序的结果,

然后再按照a进行排序,才得到下面的结果:

         A B          ROW_NUMBER()OVER(ORDERBYB)
---------- ---------- --------------------------
         1 one                                 3
         4 four                                2
         5 five                                1
        13 thirteen                            4
        22 twenty two                          5

2.row_number() over (partition by col_n[,col_m ...] order by col_1[,col_2 ...])

作用:先按照col_n[,col_m ...进行分组,

再在每个分组中按照col_1[,col_2 ...]进行排序(升序),

最后返回排好序后的结果集:

with row_number_test as(
     select 22 a,'twenty two' b,'*' c from dual union all
     select 1,'one','+' from dual union all
     select 13,'thirteen','*' from dual union all
     select 5,'five','+' from dual union all
     select 4,'four','+' from dual)
select a,b,
       row_number() over (partition by c order by b) row_number
from row_number_test
order by a;

这个例子中，我们先按照c列分组，分为2组('*'组,'+'组)，

再按照每个小组的b列进行排序(按字符串首字母的ascii码排),

最后按照a列排序,得到下面的结果集:

         A B          ROW_NUMBER
---------- ---------- ----------
         1 one                 3
         4 four                2
         5 five                1
        13 thirteen            1
        22 twenty two          2

原文：http://www.adp-gmbh.ch/ora/sql/analytical/row_number.html