Consider using LISTAGG function in case you're on 11g:
select grp, listagg(name,',') within group( order by name )
from name_table group by grp
sqlFiddle
upd: In case you're not, consider using analytics:
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
