关于oracle 的行列转换

今天才发现了wmsys.wm_concat这个有趣有用的函数，它的作用是以','链接字符。
例子如下：
SQL> create table idtable (id number,name varchar2(30));
Table created
SQL> insert into idtable values(10,'ab');
1 row inserted
SQL> insert into idtable values(10,'bc');
1 row inserted
SQL> insert into idtable values(10,'cd');
1 row inserted
SQL> insert into idtable values(20,'hi');
1 row inserted
SQL> insert into idtable values(20,'ij');
1 row inserted
SQL> insert into idtable values(20,'mn');
1 row inserted
SQL> select * from idtable;
        ID NAME
---------- ------------------------------
        10 ab
        10 bc
        10 cd
        20 hi
        20 ij
        20 mn
6 rows selected
SQL> select id,wmsys.wm_concat(name) name from idtable
  2  group by id;
        ID NAME
---------- --------------------------------------------------------------------------------
        10 ab,bc,cd
        20 hi,ij,mn
SQL> select id,wmsys.wm_concat(name) over (order by id) name from idtable;
        ID NAME
---------- --------------------------------------------------------------------------------
        10 ab,bc,cd
        10 ab,bc,cd
        10 ab,bc,cd
        20 ab,bc,cd,hi,ij,mn
        20 ab,bc,cd,hi,ij,mn
        20 ab,bc,cd,hi,ij,mn
6 rows selected
SQL> select id,wmsys.wm_concat(name) over (order by id,name) name from