SELECT a.department_id "Department",
   a.num_emp/b.total_count "%_Employees",
   a.sal_sum/b.total_sal "%_Salary"
FROM
(SELECT department_id, COUNT(*) num_emp, SUM(salary) sal_sum
   FROM employees
   GROUP BY department_id) a,
(SELECT COUNT(*) total_count, SUM(salary) total_sal
   FROM employees) b
ORDER BY a.department_id;
---------------------------
SELECT a.department_id AS "Department", a.num_emp / b.total_count AS "%_Employees", a.sal_sum / b.total_sal AS "%_Salary"
FROM (
	SELECT department_id, COUNT(*) AS num_emp, SUM(salary) AS sal_sum
	FROM employees
	GROUP BY department_id
) a, (
	SELECT COUNT(*) AS total_count, SUM(salary) AS total_sal
	FROM employees
) b
ORDER BY a.department_id;