Comma separated list into rows -opposite to listagg

with xxx as
(select 'a,b,c,d' col1 from dual)
select regexp_substr(col1,'[^,]+',1,level) result
from xxx
connect by level = length(regexp_replace(col1,'[^,]+')) +1;

Turns a,b,c,d
into rows
a
b
c
d