oracle 下实现累计求和

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列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开时排序）． 

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()l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 ．

lag（arg1,arg2,arg3): 

 

 arg1是从其他行返回的表达式

arg2是希望检索的当前行分区的偏移量。是一个正的偏移量，时一个往回检索以前的行的数目。

arg3是在arg2表示的数目超出了分组的范围时返回的值。

在oracle开发过程中经常会遇到累加、减、乘、除的问题。

下面对这个做个小的总结

--创建测试表

create table aspen(parent_id number,part_id number,qnty number);

insert into aspen values(1,1,2);

insert into aspen values(1,2,3);

insert into aspen values(1,3,2);

insert into aspen values(1,4,5);

insert into aspen values(2,2,3);

insert into aspen values(2,3,5);

insert into aspen values(2,4,7);

--实现累加

select parent_id,part_id,qnty,

sum(qnty) over(partition by parent_id order by part_id) running_prod

from aspen

 

 PARENT_ID    PART_ID       QNTY RUNNING_PROD

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

         1          1          2            2

         1          2          3            5

         1          3          2            7

         1          4          5           12

         2          2          3            3

         2          3          5            8

         2          4          7           15

--实现累减

select parent_id,part_id,qnty,

 sum(decode(rn,1,qnty,-qnty)) over(partition by parent_id order by part_id) running_prod

from (select parent_id,part_id,qnty,

      row_number() over(partition by parent_id order by part_id) rn

      from aspen)

 PARENT_ID    PART_ID       QNTY RUNNING_PROD

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

         1          1          2            2

         1          2          3           -1

         1          3          2           -3

         1          4          5           -8

         2          2          3            3

         2          3          5           -2

         2          4          7           -9

--实现累乘

select parent_id,part_id,

exp(sum(ln(qnty)) over(partition by parent_id order by part_id)) running_prod

from aspen

PARENT_ID    PART_ID RUNNING_PROD

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

        1          1            2

        1          2            6

        1          3           12

        1          4           60

        2          2            3

        2          3           15

        2          4          105

--实现累除

select parent_id,part_id,

exp(sum(decode(rn,1,ln(qnty),-ln(qnty))) over(partition by parent_id order by part_id)) running_prod

from (select parent_id,part_id,qnty,

      row_number() over(partition by parent_id order by part_id) rn

      from aspen )

 PARENT_ID    PART_ID RUNNING_PROD

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

         1          1            2

         1          2   .666666667

         1          3   .333333333

         1          4   .066666667

         2          2            3

         2          3           .6

         2          4   .085714286

row_number() OVER (PARTITION BY COL1 ORDER BY COL2) 和sum(qnty) over(partition by parent_id order by part_id) 可实现累加，其余类似。