Sum of 6 previous rows SQL SERVER 2008

Question

I have a simple query:

Select
fiscalweek, 4171
From table

And I get results in order of fiscal week:

FiscalWeek  4171
1           691
2           746
3           650
4           625
5           788
6           581
7           597
8           772
9           777

I want in a third column, the sum of the previous 6 fiscal weeks, or for week 2 just the sum of weeks 1 & 2,

so the out put would be:

FiscalWeek  4171    Sum
1           691     691
2           746     1437
3           650     2087
4           625     2712
5           788     7671
6           581     4081
7           597     3393
8           772     4013
9           777     4140

I have tried using rows unbounded preceeding but this was not available on 2008, any suggestions ?

Answer 1

The easy way, for this simple case, is a self table non equijoin. Lets supose t is your table and a is FiscalWeek:

SQL Fiddle

MS SQL Server 2014 Schema Setup :

create table t ( a int, t int);
insert into t values 
(1,10),
(2,11),
(3,12),
(4,13),
(5,14),
(6,15),
(7,16),
(8,17),
(9,18),
(10,19),
(11,20),
(12,10);

Query 1 :

select t1.a, t1.t, sum(t2.t)
from t t1
inner join t t2 
  on t2.a between t1.a-6 and t1.a --self non equijoin taking 6 prev.
group by t1.a, t1.t
order by t1.a

Results :

|  a |  t |     |
|----|----|-----|
|  1 | 10 |  10 |
|  2 | 11 |  21 |
|  3 | 12 |  33 |
|  4 | 13 |  46 |
|  5 | 14 |  60 |
|  6 | 15 |  75 |
|  7 | 16 |  91 |
|  8 | 17 |  98 |
|  9 | 18 | 105 |
| 10 | 19 | 112 |
| 11 | 20 | 119 |
| 12 | 10 | 115 |

The hard approach, may be more sql XXI century friendly or not, is to deal with CTE, partitions and ranks. Search about it if you are interesting.