需求：存在左圖銷量表，要得到右邊的保有量表，保有量等于前12月銷量和。

年

月

銷量

年

月

保有量

2010

1

4

2010

1

4

2010

2

4

2010

2

8

2010

3

4

2010

3

16

2010

4

4

2010

4

20

2010

5

4

2010

5

24

2010

6

4

2010

6

28

2010

7

4

2010

7

32

2010

8

4

2010

8

36

2010

9

4

2010

9

40

2010

10

4

2010

10

44

2010

11

4

2010

11

48

2010

12

4

2010

12

52

2011

1

4

2011

1

52

2011

2

4

2011

2

52

2011

3

4

2011

3

52

2011

4

4

2011

4

52

2011

5

4

2011

5

52

2011

6

4

2011

6

52

解答：創(chuàng)建例表，便于測試

create table tsales(y,m,n)--年，月，銷量

as select? 2010,? 1,? 4 from dual union all

select? 2010,? 2,? 4 from dual union all

select? 2010,? 3,? 4 from dual union all

select? 2010,? 4,? 4 from dual union all

select? 2010,? 5,? 4 from dual union all

select? 2010,? 6,? 4 from dual union all

select? 2010,? 7,? 4 from dual union all

select? 2010,? 8,? 4 from dual union all

select? 2010,? 9,? 4 from dual union all

select? 2010,? 10,? 4 from dual union all

select? 2010,? 11,? 4 from dual union all

select 2010, 12, 4 from dual union all

select? 2011,? 1,? 4 from dual union all

select? 2011,? 2,? 4 from dual union all

select? 2011,? 3,? 4 from dual union all

select? 2011,? 4,? 4 from dual union all

select? 2011,? 5,? 4 from dual union all

select 2011, 6, 4 from dual

--計(jì)算保有量(保有量等于前12個(gè)月內(nèi)的銷量和)

select t1.*,(select sum(t2.n)

from?tsales t2

where (t2.y = t1.y and t2.m <= t1.m)

or (t2.y = t1.y - 1 and t2.m > t1.m)

) as 保有量 from?tsales t1

--利用分析函數(shù)也可以：

--方法一

select?y,m,n,n+LAG(n,11,0)over(order by y,m)+LAG(n,10,0)over(order by y,m)+LAG(n,9,0)over(order by y,m)+

LAG(n,8,0)over(order by y,m)+LAG(n,7,0)over(order by y,m)+LAG(n,6,0)over(order by y,m)+

LAG(n,5,0)over(order by y,m)+LAG(n,4,0)over(order by y,m)+LAG(n,3,0)over(order by y,m)+

LAG(n,2,0)over(order by y,m)+LAG(n,1,0)over(order by y,m) as 保有量from tsales

--方法二

SELECT y,m,n,SUM(n)over(order by y,m rows between 11 preceding and 0 following) QTY

FROM tsales

以上兩個(gè)分析函數(shù)的使用存在錯(cuò)誤，保有量的計(jì)算是按鈕年月前推12個(gè)月(即一年內(nèi))，實(shí)際業(yè)務(wù)中不能保證每個(gè)月都有數(shù)據(jù)(即每個(gè)月都有銷量)，如果我們能確保表中每個(gè)月都有銷量的話(或?qū)⑷笔〉脑路輼?gòu)造成0銷量也可)上述兩個(gè)分析函數(shù)的方法可以使用。使用range窗體子句才是正解，如下：

SELECT y,m,n,SUM(n)over(order by y,mrange between 11 preceding and 0 following) QTY.

FROM tsales

分析函數(shù)中窗口子句rows和range的區(qū)別就是前者以記錄數(shù)分窗，后者以字段值分窗；

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