当天：
select * from T_news where datediff(day,addtime,getdate())=0
最近三天：
select * from T_news where datediff(day,addtime,getdate())<= 2 and datediff(day,addtime,getdate())>= 0
本周：
select * from T_news WHERE (DATEPART(wk, addtime) = DATEPART(wk, GETDATE())) AND (DATEPART(yy, addtime) = DATEPART(yy, GETDATE()))
注意：此时不能用 datediff 差值为7,因为，datediff只表示间隔数
本月：
select * from T_news WHERE (DATEPART(yy, addtime) = DATEPART(yy, GETDATE())) AND (DATEPART(mm, addtime) = DATEPART(mm, GETDATE()))
最近一个月：
select * from T_news WHERE (DATEPART(yy, addtime) = DATEPART(yy, GETDATE()))
AND ((DATEPART(mm, addtime) = DATEPART(mm, GETDATE())) OR (31-DATEPART(DD,addtime)+DATEPART(DD, GETDATE()))<=31)
本季度：
select * from T_news where DATEPART(qq, addtime) = DATEPART(qq, GETDATE()) and DATEPART(yy, addtime) = DATEPART(yy, GETDATE())