sqlの日付を調べます。

       ：select * from    where DateDiff(dd,datetime    ,getdate())=0
       ：select * from    where DateDiff(dd,datetime    ,getdate())=1
7       ：select * from    where DateDiff(dd,datetime    ,getdate())<=7
30       ：select * from    where DateDiff(dd,datetime    ,getdate())<=30
       ：select * from    where DateDiff(mm,datetime    ,getdate())=0
       ：select * from    where DateDiff(yy,datetime    ,getdate())=0
 
 
           ： select datepart(dayofyear,getDate())
           ：1. select datepart(dd, getDate()) 
                        2.select day(getDate())
              （  ：         ，             。           ） SELECT DATEADD(wk,DATEDIFF(wk,0,getdate()),0)
 
      ：select convert(char,dateadd(DD,-1,getdate()),111)  //111    ，（100-114）
 
         ：Select DATEADD(mm, DATEDIFF(mm,0,getdate()), 0) as firstday
          ：Select dateadd(ms,-3,DATEADD(mm, DATEDIFF(m,0,getdate())+1, 0)) as lastday      //  -3         
 
      ：select datepart(dd,dateadd(dd,-1,dateadd(mm,1,cast((cast(year(getdate()) as varchar)+'-'+cast(month(getdate()) as varchar)+'-01' ) as datetime ))))
 
          ：select datediff(day,'2012/8/1','2012/8/20') as daysum
       ±N ：select convert(char,dateadd(dd,1,'2012/8/20'),111) as riqi    //  2012/8/21
       ±N  ：select dateadd(mi,-15,getdate())  //      15       
          ： select dateadd(day,3,'20151105')   //  2015-11-08 00:00:00.000​