在线等，求平均数高效sql语句

Question

create table t_AvgDemo
(
  DevId int,
  DevName nvarchar(20),
  DataType nvarchar(20),
  RealData float,
  CurrentTime datetime,
  constraint[PK_AvgDemo_DC] primary key clustered(DevId,CurrentTime)
)
goinsert into t_AvgDemo values(1,'蓄电池A','电流A',110.2,'2012-07-23 08:20:05')
insert into t_AvgDemo values(1,'蓄电池A','电流A',111.5,'2012-07-23 08:20:28')
insert into t_AvgDemo values(1,'蓄电池A','电流A',112.3,'2012-07-23 08:20:56')
insert into t_AvgDemo values(1,'蓄电池A','电流A',109.2,'2012-07-23 08:21:05')
insert into t_AvgDemo values(1,'蓄电池A','电流A',108.3,'2012-07-23 08:21:35')
insert into t_AvgDemo values(1,'蓄电池A','电流A',110.9,'2012-07-23 08:21:50')insert into t_AvgDemo values(1,'蓄电池A','电流B',113.2,'2012-07-23 08:20:10')
insert into t_AvgDemo values(1,'蓄电池A','电流B',115.5,'2012-07-23 08:20:15')
insert into t_AvgDemo values(1,'蓄电池A','电流B',114.3,'2012-07-23 08:20:30')
insert into t_AvgDemo values(1,'蓄电池A','电流B',109.2,'2012-07-23 08:21:10')
insert into t_AvgDemo values(1,'蓄电池A','电流B',110.3,'2012-07-23 08:21:40')
insert into t_AvgDemo values(1,'蓄电池A','电流B',114.9,'2012-07-23 08:21:55')--要求为：
-- DevId   DevName   DataType  RealData     CurrentTime
--  1      蓄电池A    电流A     111.3     2012-07-23 08:20:00
--  1      蓄电池A    电流A     109.5     2012-07-23 08:21:00
--  1      蓄电池B    电流B     114.3     2012-07-23 08:20:00
--  1      蓄电池B    电流B     111.5     2012-07-23 08:21:00--求解 ？

Answer 1

SELECT DevId ,DevName, DataType,avg( RealData )RealData ,convert(char(17),CurrentTime,120)+'00'
from tb
group by
 DevId ,DevName, DataType,convert(char(17),CurrentTime,120)+'00'

Answer 2

select
 decid,devname,datatype,avg(realdata) as realdate,currenttime
from
 t_AvgDemo 
group by
 decid,devname,datatype,currenttime

Answer 3

SELECT  DevId,DevName,DataType,ROUND(AVG(RealData),1),LEFT(CurrentTime,17) + '00'
FROM t_AvgDemo
GROUP BY DevId,DevName,DataType,LEFT(CurrentTime,17)