-- This running total uses a triangular join.
-- The performance of TJ's usually sucks. Depending 
-- on the maximum number of rows which are 
-- aggregated when month = 12, you may have to change 
-- this part of the query to a running totals rCTE
-- or a Quirky Update
;WITH RunningTotals AS (
SELECT t1.cod, t1.year, t1.month, [value] = x.value 
FROM Table_1 t1
CROSS APPLY (
	SELECT value = SUM(value) 
	FROM Table_1 t2 
	WHERE t2.cod = t1.cod
	AND t2.year = t1.year	
	AND t2.month <= t1.month) x
),
-- construct a matrix containing all cod/year/month values
AllCodPeriods AS (
	SELECT 
		AllCods.cod, 
		AllYears.year, 
		AllMonths.month 
	FROM (SELECT month FROM RunningTotals GROUP BY month) AllMonths
	CROSS JOIN (SELECT year FROM RunningTotals GROUP BY year) AllYears
	CROSS JOIN (SELECT cod FROM RunningTotals GROUP BY cod) AllCods 
)
SELECT 
	matrix.cod, 	
	matrix.year, 
	matrix.month,
	ty.value, 
	[value pp] = ly.value 
FROM AllCodPeriods matrix
LEFT JOIN RunningTotals ty
	ON ty.cod = matrix.cod
	AND ty.year = matrix.year
	AND ty.month = matrix.month
LEFT JOIN RunningTotals ly 
	ON ly.cod = matrix.cod
	AND ly.year+1 = matrix.year 
	AND ly.month = matrix.month


-- here's an alternative using APPLY, which carries down
-- the running total from 2012/2 to 2012/3.
SELECT 
	AllCods.cod, 
	AllYears.year, 
	AllMonths.month,
	ty.Value,
	[value pp] = ly.value 
FROM (SELECT month FROM Table_1 GROUP BY month) AllMonths
CROSS JOIN (SELECT year FROM Table_1 GROUP BY year) AllYears
CROSS JOIN (SELECT cod FROM Table_1 GROUP BY cod) AllCods
OUTER APPLY (
	SELECT value = SUM(value) 
	FROM Table_1 t2 
	WHERE t2.cod = AllCods.cod
		AND t2.year = AllYears.year	
		AND t2.month <= AllMonths.month
) ty
OUTER APPLY (
	SELECT value = SUM(value) 
	FROM Table_1 t2 
	WHERE t2.cod = AllCods.cod
		AND t2.year+1 = AllYears.year	
		AND t2.month <= AllMonths.month
) ly