if OBJECT_ID('test')is not null
drop table test
go
create table test(
[year] int,
[month] int
)
go
insert test
select 2011,8 union all
select 2011,9 union all
select 2011,10 union all
select 2011,11 union all
select 2011,12 union all
select 2012,1 union all
select 2012,2 union all
select 2012,3 union all
select 2012,4 union all
select 2012,5 union all
select 2012,6 union all
select 2012,7 union all
select 2012,8 union all
select 2012,9
go


select * from test 
where [year]=case when month(GETDATE())<>1 
then year(getdate()) else year(getdate())-1 end
and [month]=(case when month(GETDATE())=1 then 12 else month(GETDATE())-1 end)
/*
year    month
-----------------
2012    5
*/