declare @table table(id int,y_month datetime,num int)
insert into @table 
select 0,'2009-12-1',519 union all
select 0,'2009-2-1',463 union all
select 0,'2009-9-1',723 union all
select 0,'2010-1-1',199 union all
select 0,'2010-8-1',371 union all
select 0,'2011-1-1',278 union all
select 0,'2011-12-1',437 union all
select 0,'2011-2-1',441 union all
select 1,'2009-1-1',370 union all
select 1,'2009-9-1',230 union all
select 1,'2010-1-1',247 union all
select 1,'2011-11-1',821 union all
select 2,'2009-1-1',836 union all
select 2,'2010-8-1',416 union all
select 2,'2011-9-1',799 

select 
id, 
datepart(month,y_month) month,
sum(case when datepart(year,y_month) = 2009 then num else 0 end) as '2009',
sum(case when datepart(year,y_month) = 2010 then num else 0 end) as '2010',
sum(case when datepart(year,y_month) = 2011 then num else 0 end) as '2011'
from @table
group by
id, 
datepart(month,y_month)
order by
id,
datepart(month,y_month)

------解决方案--------------------
sum汇总一下就好了