How to Display Multiple rows in one single row?

SELECT rtrim (xmlagg (xmlelement (D, TASK_NUMBER || ',')).extract ('//text()'), ',') enames
FROM PA_TASKS T
WHERE TASK_ID NOT IN (SELECT TASK_ID FROM
PA_PROJECT_FUNDINGS C
WHERE C.PROJECT_ID=82)
AND T.PROJECT_ID=82


select
   deptno,
   rtrim (xmlagg (xmlelement (e, ename || ',')).extract ('//text()'), ',') enames
from
   dual
group by
   deptno
;