学步园

Declare @i int,@t1 datetime , @t2 datetime;
select @i = 0, @t1 = getdate();
while @i<1000000
begin
declare @BeginDate datetime, @EndDate datetime
-- 方法1，用datediff
select @BeginDate = cast(datediff(day, 0, getdate()) as datetime)
     , @EndDate = dateadd(ms,-2,datediff(day,-1,getdate()))  
--select @BeginDate datetime, @EndDate
set @i=@i+1
end
select @t2 = getdate();
print convert(nvarchar(100), convert(float, @t2-@t1))
go




Declare @i int,@t1 datetime , @t2 datetime;
select @i = 0, @t1 = getdate();
while @i<1000000
begin
declare @BeginDate datetime, @EndDate datetime
-- 方法2，获取当前天数来计算
select @BeginDate = ROUND (CONVERT(float, getdate()),0,1)  -- 获取日期部分 2008-05-01 00:00:00.000
     , @EndDate = @BeginDate + .999999999                -- 计算日期最后一秒 2008-05-01 23:59:59.997
--select @BeginDate datetime, @EndDate
set @i=@i+1
end
select @t2 = getdate();
print convert(nvarchar(100), convert(float, @t2-@t1))

测试结果

7.8125e-005
7.24923e-005
第二种会比第一种方法快那么一点,呵呵.

其实计算为2天的范围更好
'2008-06-01 00:00:00.000' '2008-06-02 00:00:00.000' 

比较时用 CreatTime >= @begin and CreateTime < @end