select * from tb where col>='2008-05-16' and col<'2008-05-17'

where datediff(dd,字段,'2008-05-16')==0
--或者
where convert(varchar(10),日期,120)='2008-05-16'

select * from tb where col>='2008-05-16 10:00:00' and col<'2008-05-16 11:00:00'

where convert(varchar(10),日期,120)='2008-05-16'

where 日期 like '2008-05-16%' 

select * from tb 
where 日期 between '2008-05-16 10:00:00' and '2008-05-16 11:00:00'
order by 日期