declare
cursor cursor1 is select department_id,department_name from departments order by department_id;
variable1 varchar2(256);
variable2 varchar2(256);

begin
for x in cursor1 loop
  for t in (  select
              employees.employee_id
              from employees
              where x.department_id=employees.DEPARTMENT_ID ) loop
              
              variable1 := t.employee_id;
              dbms_output.put(variable1||', ');
  end loop;
variable2 := x.DEPARTMENT_ID||'. ';
dbms_output.put_line(variable2);
end loop;
end;
/ 
 

for x in cursor1 loop
  dbms_output.put_line(x.department_id);
  for t in (...)

SQL> select d.deptno||'. '||listagg(e.empno,', ') within group (order by e.empno) res
  2  from dept d, emp e
  3  where e.deptno (+) = d.deptno
  4  group by d.deptno
  5  order by d.deptno
  6  /
RES
--------------------------------------------------------------------------------------
10. 7782, 7839, 7934
20. 7369, 7566, 7788, 7876, 7902
30. 7499, 7521, 7654, 7698, 7844, 7900
40.

4 rows selected.

SQL> ed
Wrote file afiedt.buf

  1  declare
  2    empnos  varchar2(1000);
  3  begin
  4  for rec in (select deptno from dept order by 1)
  5  loop
  6  select wm_concat(empno) res
  7    into empnos
  8    from emp
  9   where deptno (+) = rec.deptno;
 10  dbms_output.put_line (rec.deptno||', '||empnos);
 11  end loop;
 12* end;
SQL> /
10, 7782,7839,7934
20, 7369,7566,7788,7876,7902
30, 7499,7521,7654,7698,7844,7900
40,

PL/SQL procedure successfully completed.

SQL> 

SQL> select a.deptno, wm_concat(empno) res
  2    from dept a, emp b
  3   where b.deptno (+) = a.deptno
  4   group by a.deptno
  5   order by 1;

   DEPTNO RES
--------- -----------------------------------
       10 7782,7934,7839
       20 7566,7788,7369,7876,7902
       30 7521,7654,7698,7900,7499,7844
       40

4 rows selected.

SQL>