What are the department ids, full names, and salaries for employees who make the most in their departments?
SELECT first_name ,   last_name ,   salary ,  department_id ,  MAX(salary) FROM employees GROUP BY department_id
make the most in their departments refers to MAX(salary) for each department; department ids, full names, and salaries refers to department_id, CONCAT(first_name, ' ', last_name) as full_name, and salary;