SQL中取得时间的一些技巧

*********在Sql Server中时间是精确到3毫秒*****************
--------------第一天---------------------------------------
SELECT DATEADD(mm, DATEDIFF(mm,0,getdate()), 0)

select DATEDIFF(mm,0,getdate())

SELECT DATEADD(wk, DATEDIFF(wk,0,getdate()), 0)
SELECT DATEADD(yy, DATEDIFF(yy,0,getdate()), 0)
SELECT DATEADD(qq, DATEDIFF(qq,0,getdate()), 0)


--------------当天半夜--------------------------------------------
SELECT DATEADD(dd, DATEDIFF(dd,0,getdate()), 0)

--------------最后一天--------------------------------------------
SELECT dateadd(ms,-3,DATEADD(mm, DATEDIFF(mm,0,getdate()), 0))
SELECT dateadd(ms,-3,DATEADD(yy, DATEDIFF(yy,0,getdate()), 0))
SELECT dateadd(ms,-3,DATEADD(mm, DATEDIFF(m,0,getdate())+1, 0))
SELECT dateadd(ms,-3,DATEADD(yy, DATEDIFF(yy,0,getdate())+1, 0))

select DATEADD(wk, DATEDIFF(wk,0,dateadd(dd,6-datepart(day,getdate()),getdate())),0)


----------去掉时分秒----------------------------
declare @a datetime 
set @a = getdate()
SELECT @a,DATEADD(day,DATEDIFF(day,0,@a),0)
　　
----------显示星期几----------------------------
select datename(weekday,getdate())
　　
----------如何取得某个月天数-------------------
declare @m int
set @m=3 --月份
select datediff(day,'2006-'+cast(@m as varchar)+'-15' ,'2006-'+cast(@m+1 as varchar)+'-15')
　　
----------或者使用计算本月的最后一天的脚本，然后用DAY函数区最后一天
SELECT Day(dateadd(ms,-3,DATEADD(mm, DATEDIFF(m,0,getdate())+1, 0)))

----------判断是否闰年：------------------------
SELECT case day(dateadd(mm, 2, dateadd(ms,-3,DATEADD(yy, DATEDIFF(yy,0,getdate()), 0)))) when 28 then '平年' else '闰年' end

select case datediff(day,datename(year,getdate())+'-02-01',dateadd(mm,1,datename(year,getdate())+'-02-01')) 
when 28 then '平年' else '闰年' end
　　
----------一个季度多少天------------------------
declare @m tinyint,@time smalldatetime
select @m=month(getdate())
select @m=case when @m between 1 and 3 then 1
when @m between 4 and 6 then 4
when @m between 7 and 9 then 7
else 10 end
select @time=datename(year,getdate())+'-'+convert(varchar(10),@m)+'-01'
select datediff(day,@time,dateadd(mm,3,@time))