oracle排序一个挺有用的东西

update tChnAssSetGroupGrade c set c.assposition = (select d.rank from ( select b.group_id,b.sorce,b.assposition,rownum rank from (select a.group_id,a.sorce,a.assposition from tChnAssSetGroupGrade a order by a.sorce desc)b )d where d.group_id=c.group_id);