sql server 2000中怎么按时间分组筛选数据_Sql Server

sql server 2000中怎样按时间分组筛选数据
表格结构

现在想按每小时取出一个ReadNumber（取每小时最小的）由于是软件自动生成的数据 ReadDate数据类型是varchar
求具体写法用的是sel server 2000

------解决方案--------------------

SQL code

select * from tb as t where not exists(select 1 from tb where convert(varchar(13),ReadDate,120)=convert(varchar(13),ReadDate,120)and ReadNumber<t.ReadNumber)
------解决方案--------------------
SQL codeselect convert(decimal(18,12),                replace(min(convert(char(13),readdate,120)+convert(varchar(18),ReadNumber)),                        min(convert(char(13),readdate,120)),                        '')                )from tabgroup by convert(char(13),readdate,120)
------解决方案--------------------
SQL codeselect convert(varchar(10),ReadyDate,120) 日期,datepart(hh,ReadyDate) 小时,min(ReadNumber) ReadNumber from [表]group by convert(varchar(10),ReadyDate,120),datepart(hh,ReadyDate)