split a string into multiple lines by comma

SQL> select c2 from test;

C2
----------------------------------------
a,b,c,dd,efg
h,iii


select
decode(lvl, 1, substr(c2, 1, instr(c2, ',', 1) - 1),
length(c2) - length(replace(c2, ',')) + 1, substr(c2, instr(c2, ',', 1, lvl-1)+1),
substr(c2, instr(c2, ',', 1, lvl-1) + 1, instr(c2, ',', 1, lvl) - instr(c2, ',', 1, lvl-1) -1))
what_you_need
from
(
select level lvl from (select max(length(c2) - length(replace(c2, ','))) + 1 maxlvl from test)
connect by 1 = 1 and level <= maxlvl
),
test
where lvl < length(c2) - length(replace(c2, ',')) + 2
/

WHAT_YOU_NEED
-------------
a
b
c
dd
efg
h
iii