求按时段统计sql查询语句,高手帮帮忙啊

SELECT year(t.dt) as 年,month(t.dt) as 月,day(t.dt) as 日,b.h as 时,count(*) as 访问数 

from t1 t right join(

select distinct hour(dt) as h from t1

)b on hour(t.dt)=b.h

where not exists(select 1 from t1 where ip=t.ip and year(dt)=year(t.dt) 

and month(dt)=month(t.dt) and day(dt)=day(t.dt) and hour(dt)<hour(t.dt))

group by year(dt),month(dt),day(dt),b.h

SELECT year(dt) as 年,month(dt) as 月,day(dt) as 日,hour(dt) as 时,count(*) as 访问数 

from t1 

group by year(dt),month(dt),day(dt),hour(dt)

select hour(日期),count(*)

from 表如下：

group by hour(日期)

    ip                   日期

42.168.2.5        2011-10-23 00:17:21

88.68.23.56       2011-10-23 00:57:21

142.68.4.33       2011-10-23 01:11:26

192.138.2.6       2011-10-23 01:26:22

92.178.22.57      2011-10-23 08:40:25

132.188.21.205    2011-10-23 12:30:28

195.148.28.58     2011-10-23 14:26:23

182.128.82.95     2011-10-23 23:27:29