-->测试数据
declare @table table([N] int,[Y] int,[R] int)
insert into @table
select '2012','08','20' union all
select '2012','09','05' union all
select '2012','09','06' 


--select *  from @table

-->测试查询
select convert(varchar,[N])+'-'+convert(varchar,[Y])+'-'+convert(varchar,[R])as 日期 
from @table 
where convert(varchar,[N])+'-'+convert(varchar,[Y])+'-'+convert(varchar,[R])<= convert(varchar,'2012-9-6')

-->测试结果
/*
---------------------------------------
日期
2012-8-20
2012-9-5
2012-9-6

*/