Com um pouco de ajuda do XML, você pode fazer funcionar. O exemplo é baseado no esquema de RH.
SQL> select
2 listagg(s.department_name, ',') within group (order by null) result
3 from departments s, departments d;
from departments s, departments d
*
ERROR at line 3:
ORA-01489: result of string concatenation is too long
SQL>
SQL> select
2 rtrim(xmlagg(xmlelement (e, s.department_name || ',')).extract
3 ('//text()').getclobval(), ',') result
4 from departments s, departments d;
RESULT
--------------------------------------------------------------------------------
Administration,Administration,Administration,Administration,Administration,Admin
SQL>
