En Oracle 11g, puede usar LISTAGG() función:
select id,
number,
listagg(letter, ', ') within group(order by id, number) as letter
from yourtable
group by id, number;
Consulte SQL Fiddle con demostración
En Oracle 11g, puede usar LISTAGG() función:
select id,
number,
listagg(letter, ', ') within group(order by id, number) as letter
from yourtable
group by id, number;
Consulte SQL Fiddle con demostración