How to print data from multiple rows as a single field

Using LISTAGG:
 
SELECT deptno,listagg(ename,',') within group (order by deptno) employees
from emp group by deptno;

Using COLLECT:

SELECT DEPTNO, TO_STRING(CAST( COLLECT(ENAME) AS VARCHAR2_NTT)) AS EMPLOYEES  FROM EMP GROUP BY DEPTNO