SELECT count(employee_id) headcount FROM employees;
SELECT department_id, count(employee_id) headcount FROM employees GROUP BY department_id HAVING headcount >= 5
SELECT d.department_name FROM departments AS d
SELECT employee_id, first_name, last_name, department_name FROM employees INNER JOIN departments ON department_id = department_id ORDER BY first_name;
SELECT employee_id, first_name, last_name, employees.department_id, department_name FROM employees INNER JOIN departments ON departments.department_id = employees.department_id ORDER BY first_name;
SELECT employee_id, first_name, last_name, e.department_id, department_name FROM employees e INNER JOIN departments d ON d.department_id = e.department_id ORDER BY first_name;
SELECT e.first_name AS employee, m.first_name AS manager FROM employees e LEFT JOIN employees m ON m.employee_id = e.manager_id ORDER BY manager;