表为：
列名：站号，模式名，偏差，日期，要素
试图查询每个站中最小的那个偏差的模式名
create table B as SELECT stationid,min(abserror) as minabserror FROM `spotmap` WHERE element = 'tem' group by stationid 结果生成表b
SELECT * FROM b as tb inner JOIN spotmap as s on s.stationid=tb.stationid and s.abserror = tb.minabserror查出结果
