use below code:

CREATE TABLE #Table(

[cod] [nchar](10) NULL,

[year] [int] NULL,

[month] [tinyint] NULL,

[value] [float] NULL

) ON [PRIMARY]

GO

insert into #Table values ('cod1',2011,1,100)

insert into #Table values ('cod1',2011,2,150)

insert into #Table values ('cod1',2011,3,200)

insert into #Table values ('cod1',2012,1,100)

insert into #Table values ('cod1',2012,2,180)

select cod,year,month,sum(value) val

into #temp1 from

(select * from #Table t2

UNION

select t2.cod,T2.year+1,t2.month,'' ppy from #Table t2

WHERE T2.month not in(select isnull(t5.month,0) as month from #Table t5 where (T2.year-1)=T5.year)

)k

group by cod,year,month

select cod,year,month,CASE WHEN val<>0 THEN val END val,(select SUM(t1.val) from #temp1 t1 WHERE (T2.year-1)=T1.year AND T2.month>=T1.month) AS PPY from #temp1 T2