由于没有指定时间段的datetime将具有date 00:00:00.000的值，如果您希望确保获得范围内的所有日期，则必须为结束日期提供时间，或者增加结束日期并使用<。

select Date,TotalAllowance from Calculation where EmployeeId=1 
and Date between '2011/02/25' and '2011/02/27 23:59:59.999'

OR

select Date,TotalAllowance from Calculation where EmployeeId=1 
and Date >= '2011/02/25' and Date < '2011/02/28'

OR

select Date,TotalAllowance from Calculation where EmployeeId=1 
and Date >= '2011/02/25' and Date <= '2011/02/27 23:59:59.999'

不要使用下面的语句，因为如果它们的时间是00:00:00.000，它可能会返回一些从2011/02/28开始的记录。

select Date,TotalAllowance from Calculation where EmployeeId=1 
and Date between '2011/02/25' and '2011/02/28'

select Date,TotalAllowance 
from Calculation 
where EmployeeId=1
  and convert(varchar(10),Date,111) between '2011/02/25' and '2011/02/27'

Select 
    * 
from 
    Calculation 
where 
    EmployeeId=1 and Date between #2011/02/25# and #2011/02/27#;

SELECT Date, TotalAllowance  
FROM Calculation  
WHERE EmployeeId = 1 
  AND Date BETWEEN to_date('2011/02/25','yyyy-mm-dd') 
               AND to_date ('2011/02/27','yyyy-mm-dd');

我会选择

select Date,TotalAllowance from Calculation where EmployeeId=1
             and Date >= '2011/02/25' and Date < DATEADD(d, 1, '2011/02/27')

逻辑是>=包括整个开始日期，<不包括结束日期，因此我们在结束日期上添加一个单位。这可以适应几个月，例如:

select Date, ... from ...
             where Date >= $start_month_day_1 and Date < DATEADD(m, 1, $end_month_day_1)

如果日期在24小时内，从早上开始，到晚上结束，应该添加如下内容:

declare @Approval_date datetime
set @Approval_date =getdate()
Approval_date between @Approval_date +' 00:00:00.000' and @Approval_date +' 23:59:59.999'