求助，这个sql怎么写？

dwei7

免费乐捐，感谢支持

现在要按行业大类分组，求每组行业中销售额前10名的企业；
Oracle中可以这样写：

select QBXSSR as QBXSSR,HY_DM as HY_DM,NSRDZDAH as NSRDZDAH
from (
select sum(a.QBXSSR) as QBXSSR, SUBSTR(a.HY_DM,1,1) as HY_DM,a.NSRDZDAH as NSRDZDAH,
row_number() over (partition by  SUBSTR(a.HY_DM,1,1) order by sum(a.QBXSSR) desc nulls last) as NSRDZDAH_sortn
from FACT_SBXX a
where (a.NSR_SWJG_DM like '121%')
group by  SUBSTR(a.HY_DM,1,1),a.NSRDZDAH
order by  SUBSTR(a.HY_DM,1,1) nulls first) a
where (NSRDZDAH_sortn<=10)

这里用到了row_number() over (partition by  SUBSTR(a.HY_DM,1,1) order by sum(a.QBXSSR) desc nulls last)
请问Sybase IQ中这么写这个sql?