select left(songno,3) as songno from song  //截取前3位

select distinct right(left(songno,6),3) as Files from song order by Files asc    // 截取中间

select right(songno,6) as 歌曲编号 from song  //截取后3位

select left(songno,3) as 服务器编号 from song

select mapping from drivers

select left(songno,3) as songno,drivers.mapping from song left join drivers on drivers.driversid=song.songno