Oracle行转列, 列以字符串的形式进行拼接

Oracle10g提供了个新函数wmsys.wm_concat，可以完成行转列后列以字符串的形式进行拼接，如下SQL

create table aaa(
          id varchar2(20)
   )
   
   create table bbb(
          a_id varchar2(20),
          a_name varchar2(20))        
   
   insert into aaa values('a');
   insert into aaa values('b');      
   insert into bbb values('a', '1');
   insert into bbb values('a', '2');
   insert into bbb values('a', '3');
   insert into bbb values('b', '1');
                    
   select id, wmsys.wm_concat(b.a_name) str
   from aaa a, bbb b where a.id = b.a_id
   group by id