APPS-ORACLE.RU

with t as (
select 1 as id, 'a' gr from dual
union all
select 2 as id, 'a' gr from dual
union all
select 4 as id, 'b' gr from dual
)
select
 rtrim(to_char(sys_xmlagg(xmlelement(id,id ||',')).extract('/ROWSET/ID/text()').getclobval()),',') TEXT
from t
group by gr;

TEXT
-------
1,2
4