这样的查询如何实现？

我现在有2张表，一张学生等级表GradeInfo，分别有gradeId，mc2个字段，还有张表学生表stuInfo，stuId,mc,gradeId(外键),我想查询每个等级下得对应的学生，
效果是这样的
GradeMc stuMc
  A jack,mali,marry
  B tony,sack,tome
  c kay,jimy

各位大侠看下！

SQL code

select a.mc GradeMc,wm_concat(b.mc) stuMc from GradeInfo a,stuInfo b
where GradeInfo.gradeId = stuInfo.gradeId group by GradeInfo.mc

SQL code

就是行转列的用法!

给出具体的数据!

wm_concat这个函数有么？如何理解？

SQL code

with a as
(
     select 1 gradeId,'A'mc2 from dual
     union all
     select 2 gradeId,'B'mc2 from dual
     union all
     select 3 gradeId,'C'mc2 from dual
),
b as
(select 1 gradeId,'jack' stuInfo from dual
 union all
 select 1,'mali' from dual
 union all
 select 1,'marry' from dual
 union all
 select 2,'tony' from dual
 union all
 select 2,'sack' from dual
 union all
  select 2, 'tome' from dual
  union all
  select 3 ,'kay' from dual
  union all
  select 3 ,'jimy' from dual
)
--select mc2,row_number()over(partition by a.gradeid order by a.gradeid) rn,stuinfo from a,b where a.gradeId=b.gradeId
select mc2,max(substr(sys_connect_by_path(stuinfo,','),2))  studinfo
from 
(       select mc2,a.gradeid,row_number()over(partition by a.gradeid order by a.gradeid) rn, stuinfo 
        from a,b where a.gradeId=b.gradeId   ) a
group by mc2
start with rn=1  connect by  a.gradeId = prior a.gradeId  and rn-1 = prior rn


   

1    A    jack,mali,marry
2    B    tony,sack,tome
3    C    kay,jimy