select top(10)* from
 (select
  case when ktext = '' or ktext is null then cusna else ktext end as cusna,
 sum(sr)/10000 as sr
 from xsjsc_xsmx ,xsjsc_kh
 where year = year(getdate())  and xsjsc_xsmx.cusno = xsjsc_kh.KUNNR
 group by case when ktext = '' or ktext is null then cusna else ktext end ) a
 order by sr desc

如何再不改变其他条件的情况下，添加什么条件能截取cunsa字符串的前四位字符