create table #date ( number int identity(1,1) primary key, date datetime ) insert into #date select '2009/1/11 17:00' insert into #date select '2009/1/12 12:00' insert into #date select '2009/1/12 10:00' insert into #date select '2009/1/12 4:00' insert into #date select '2009/1/11 18:00' insert into #date select '2009/1/11 12:00' insert into #date select '2009/1/11 5:00' insert into #date select '2009/1/11 2:00'
select (d2.number-d1.number) number from ( select number,date from #date where date in (select max(date) from #date group by convert(varchar(10),date,120) ) ) d1 , ( select number,date from #date where date in (select min(date) from #date group by convert(varchar(10),date,120) ) ) d2 where convert(varchar(10),d1.date,120)=convert(varchar(10),d2.date,120)