select 'Revathi ,Sharath ,Cherry , Vitech, Hyd , Chandanagr, Revathi, Vitech , XYZ , Cherry, Hyd' Single_repeation
  from dual

SQL> select deptno,
  2         rtrim(listagg(distinct  ename || ', ') within group(order by deptno)) con
  3    from scott.emp
  4   group by deptno
  5  ;
 
select deptno,
       rtrim(listagg(distinct  ename || ', ') within group(order by deptno)) con
  from scott.emp
 group by deptno
 
ORA-30482: DISTINCT option not allowed for this function
 
SQL> 

select deptno,
       listagg(.....)
  from (select distinct deptno, ename from scott.emp)

select  xmlquery(
                 'string-join(distinct-values(ora:tokenize(.," ,"))," ,")'
                 passing 'Revathi ,Sharath ,Cherry ,Vitech ,Hyd ,Chandanagr ,Revathi ,Vitech ,XYZ ,Cherry ,Hyd'
                 returning content
                ).GetStringVal() Single_repeation
  from  dual
/

SINGLE_REPEATION
-------------------------------------------------------
Chandanagr ,Cherry ,Hyd ,Revathi ,Sharath ,Vitech ,XYZ

SQL>