declare @date datetime
set @date = '2010-02-06 18:00:00'

print dateadd(dd,datediff(dd,0,@date),0) --去掉时分秒
print datediff(dd,@date,dateadd(mm,1,@date)) --本月天数
print dateadd(mm,1,dateadd(dd,-datepart(dd,@date),@date)) --本月最后一天