select *
 from tb
   where (datediff(hour,dt,getdate()) between 3 and 6) or
         (dt between '2007-12-01' and '2007-12-11')

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SQL code
select * from tb where 字段 between '2007-12-01' and '2007-12-11'

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SQL code
三小时,六小时,估计得用分钟来算才是你的本意.

select * from tb where datediff(mi,时间字段,getdate()) <= 180
select * from tb where datediff(mi,时间字段,getdate()) <= 360


2007-12-01至2007-12-11

select * from tb where convert(varchar(10),时间字段,120) between '2007-12-01' and '2007-12-11'

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SQL code
2007-12-01至2007-12-11

select * from tb where 时间字段 between '2007-12-01' and '2007-12-11'