create table data(ID int,date datetime,[1s] decimal(5,1))

insert data

select 156,'2008-08-04 14:14:46',0.0 union all

select 157,'2008-08-04 14:14:47',41.7 union all

select 158,'2008-08-04 14:14:48',44.6 union all

select 159,'2008-08-04 14:14:49',43.6 union all

select 160,'2008-08-04 14:14:50',41.9 union all

select 160,'2008-08-04 14:25:50',10.10

--------------------------------------------------

select convert(char(15),date,120)+str(datepart(mi,date)/5*5%10,1),avg([1s])

  from data

 group by convert(char(15),date,120),datepart(mi,date)/5

/*

---------------- ---------------------------------------

2008-08-04 14:10 34.360000

2008-08-04 14:25 10.100000

(2개 행 적용됨)

*/