Prendi in considerazione l'utilizzo della funzione LISTAGG nel caso in cui tu sia su 11g:
select grp, listagg(name,',') within group( order by name )
from name_table group by grp
sqlFiddle
aggiorna: In caso contrario, considera l'utilizzo di analisi:
select grp,
ltrim(max(sys_connect_by_path
(name, ',' )), ',')
scbp
from (select name, grp,
row_number() over
(partition by grp
order by name) rn
from tab
)
start with rn = 1
connect by prior rn = rn-1
and prior grp = grp
group by grp
order by grp
sqlFiddle
