How To Split Comma Separated values in oracle SQL

with t as
 (select 'NUTHAN,RAJU,RAM,CHERRY' as STR from dual)
Select Regexp_substr(STR ,'[^,]+',1,level) from T
connect by level <=regexp_count(STR,',',1)+1;

How to convert a column into comma separated values in oracle 

select rtrim(xmlagg(xmleleent('X',empno||',')).extract('//text()'),',') from emp;