SQL按天进行分组查询最大值和最小值

select CONVERT(varchar(10), datatime, 23) as edt
,(select max(cast(a1 as float)) from TB_DataMinute where dcode='12345678' 
and datatime >= CONVERT(varchar(10), datatime, 23) 
and  dateadd(day,-1,datatime)<CONVERT(varchar(10), datatime, 23)
)
,(select min(cast(a1 as float)) from TB_DataMinute where dcode='12345678' 
and datatime >= CONVERT(varchar(10), datatime, 23) 
and  dateadd(day,-1,datatime)<CONVERT(varchar(10), datatime, 23)
)
from TB_DataMinute where dcode='12345678' group by CONVERT(varchar(10), datatime, 23) 
order by edt desc;