display the department ID, full name (first and last name), salary for those employees who is highest salary in every department.
SELECT first_name ,   last_name ,   salary ,  department_id ,  MAX(salary) FROM employees GROUP BY department_id
highest salary in every department refers to MAX(salary) for each department_id; display department ID, full name (first and last name), salary refers to selecting department_id, first_name, last_name, salary;