跟当前日期比较

距离今天最早8天之内的讯息
select id, addtime,dateadd(day,8,addtime) as plus
from protuct
where dateadd(day,8,addtime)< getdate()

距离今天最早8月之内的讯息
select id, addtime,dateadd(month,8,addtime) as plus
from protuct
where dateadd(month,8,addtime)< getdate()

距离今天最早8年之内的讯息
select id, addtime,dateadd(month,8,addtime) as plus
from protuct
where dateadd(year,8,addtime)< getdate()