oracle中常用函数ROW_NUMBER() OVER()(分析函数)

row_number()over(partition by col1 order by col2)表示根据col1分组,在分组内部根据col2排序,而此函数计算的值就表示每组内部排序后的顺序编号(组内连续的唯一的)。
与rownum的区别在于:使用rownum进行排序的时候是先对结果集加入伪劣rownum然后再进行排序,而此函数在包含排序从句后是先排序再计算行号码。
row_number()和rownum差不多,功能更强一点(可以在各个分组内从1开始排序)。
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)
dense_rank()也是连续排序,有两个第二名时仍然跟着第三名。相比之下row_number是没有重复值的。

oracle 分析函数 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

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转载自blog.csdn.net/yilongzhetian/article/details/50673240