SQL To Calculate "To Date" Values With Month Columns - sql

Question

SQL Afficianados,
There has got to be a better way than the road I am going down...
SQL Fiddle HERE
Using SQL Server 2008. In short, I have a table with months as columns. i.e.:
CREATE TABLE MyData (MyID VARCHAR(10),
JAN MONEY, FEB MONEY, MAR MONEY, APR MONEY, MAY MONEY, JUN MONEY,
JUL MONEY, AUG MONEY, SEP MONEY, OCT MONEY, NOV MONEY, DEC MONEY);
Given a month value of N (as integer, where 1 = JAN and 12 = DEC), I want to calculate a "To Date" value from the first month to the Nth month.
So, given this simple data:
INSERT INTO MyData (MyID, JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC)
SELECT 'Rec1', 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
UNION ALL SELECT 'Rec2', 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
UNION ALL SELECT 'Rec3', 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
;
I want to pass in any month value and add up the proper month columns. Given the sample data above, here is a chart of expected results based on the value of the month passed in...
Month Value | Expected Result |
------------+------------------
1 | 3
2 | 9
3 | 18
4 | 30
5 | 45
6 | 63
7 | 84
8 | 108
9 | 135
10 | 165
11 | 198
12 | 234
I know I could do this with a CASE statement like this:
DECLARE #v_Month INT = 2
SELECT CASE
WHEN #v_Month = 1 THEN SUM(JAN)
WHEN #v_Month = 2 THEN SUM(JAN) + SUM(FEB)
WHEN #v_Month = 2 THEN SUM(JAN) + SUM(FEB) + SUM(MAR)
--You get the idea. The pattern would continue for the rest of the months.
ELSE 0
END AS ToDateSum
FROM MyData
But is there a better way? Teach me, oh great ones of SQL Server.

Answer 1

You can use unpivot to change the data to a more amenable shape. It might make more sense to store it this way in the first place.
declare #v_Month int = 2;
with u as (
select
myid, [month], amount
from (
select
myid, jan [1], feb [2], mar [3], apr [4], may [5], jun [6],
jul [7], aug [8], sep [9], oct [10], nov [11], dec [12]
from
MyData
) p
unpivot (
amount for [month] in ([1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12])
) u
) select
sum(amount)
from
u
where
[month] <= #v_Month;
Example SQLFiddle
You can simplify this a bit, if you want to keep the data in the same structure:
select
sum(amount)
from (
select
myid, jan [1], feb [2], mar [3], apr [4], may [5], jun [6],
jul [7], aug [8], sep [9], oct [10], nov [11], dec [12]
from
MyData
) p
unpivot (
amount for [month] in ([1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12])
) u
where
[month] <= #v_Month;

Answer 2

Something like this will work:
declare #MyDesiredMonth int = 3
with normalized_view as
(
select MyId , Month = 1 , Value = Jan from MyData
UNION ALL select MyId , Month = 2 , Value = Feb from MyData
UNION ALL ...
UNION ALL select MyId , Month = 11 , Value = Nov from MyData
UNION ALL select MyId , Month = 12 , Value = Dec from MyData
)
select MonthlyTotal = sum(Value)
from normalized_view t
where t.Month = #myDesiredMonth
Alternatively, something like this:
declare #MyDesiredMonth int = 3
select MonthlyTotal = sum( case #MyDesiredMonth
when 1 then t.Jan
when 2 then t.Feb
...
when 11 then t.Nov
when 12 then t.Dec
end
)
from MyTable t
Either one should work with the execution plan likely winding up similar.