select regexp_substr('a,b,c,d','[^,]+', 1, level) from dual connect by regexp_substr('a,b,c,d', '[^,]+', 1, level) is not null
select regexp_substr('a,b,c,d','[^,]+', 1, level) from dual connect by regexp_substr('a,b,c,d', '[^,]+', 1, level) is not null