SELECT a.dept_no, a.dept_name, sal.emp_no, sal.salary
  FROM departments a,
       (SELECT emp_no, dept_no
          FROM dept_manager
         WHERE SYSDATE() BETWEEN from_date AND to_date
       ) dept_mgr,
       (SELECT a.emp_no, a.salary, b.dept_no
          FROM salaries a, dept_mgr b
         WHERE SYSDATE() BETWEEN a.from_date AND a.to_date
           AND a.emp_no = b.emp_no
       ) sal
 WHERE a.dept_no = sal.dept_no;