SQL Query to display % Change - sql

Question

I have a database with sample data represented by Table 1 below. How do I write an SQL query to display them in either Table 2 or Table 3 format?
Table 1 Table 2
Date | Value Year | Week | Total Value | % Change
------------+------- ------+-----+--|---------------|----------
19/12/2011 | 60 2012 | 1 | 295 | 656.41%
20/12/2011 | 49 2012 | 0 | 39 | -80.98%
21/12/2011 | 42 2012 | 52 | 205 | -41.76%
22/12/2011 | 57 2011 | 51 | 352 |
23/12/2011 | 88
24/12/2011 | 18 Table 3
25/12/2011 | 38 Year | Week | SUM1 | Year | Week | SUM2 | % Change
26/12/2011 | 16 ------+--------+--------+--------+--------+--------+-----------
27/12/2011 | 66 2012 | 1 | 295 | 2012 | 0 | 39 | 656.41%
28/12/2011 | 21 2012 | 0 | 39 | 2011 | 52 | 205 | -80.98%
29/12/2011 | 79 2011 | 52 | 205 | 2011 | 51 | 352 | -41.76%
30/12/2011 | 7 2011 | 51 | 352 |
31/12/2011 | 16
01/01/2012 | 39
02/01/2012 | 17
03/01/2012 | 86
04/01/2012 | 55
05/01/2012 | 82
06/01/2012 | 0
07/01/2012 | 9
08/01/2012 | 46

Answer 1

My preference would be to run 1 query to aggregate Table 1 to the year/week level and then do the "% change" in another language, depending on your environment. However, if you truly needed a SQL-only solution, you could do something like this.
create table t1 as
select year(Date) as year, week(Date) as week, sum(Value) as totalvalue
from table1
group by year(Date) as year, week(Date) as week
order by Date desc
;
select a.year, a.month, a.totalvalue,
(a.totalvalue-b.totalvalue)/b.totalvalue as pct_change
from (
select year, month, totalvalue,
case when week>1 then week-1 else 52 end as prevweek,
case when week>1 then year else year-1 end as prevyear
from t1
) a
left outer join t1 b
on a.prevweek=b.week and a.prevyear =b.year
;