-- 内连接
SELECT last_name , department_name FROM employees e JOIN departments d
ON e.department_id = d.department_id
-- 左外连接
SELECT last_name , department_name FROM employees e LEFT JOIN departments d
ON e.department_id = d.department_id
-- 右外连接
SELECT last_name , department_name FROM employees e RIGHT JOIN departments d
ON e.department_id = d.department_id
-- 左滤连接
SELECT last_name , department_name FROM employees e LEFT JOIN departments d
ON e.department_id = d.department_id WHERE d.department_id IS NULL
-- 右滤连接
SELECT last_name , department_name FROM employees e RIGHT JOIN departments d
ON e.department_id = d.department_id WHERE e.department_id is null
-- 全连接
SELECT last_name , department_name FROM employees e LEFT JOIN departments d
ON e.department_id = d.department_id
UNION ALL
SELECT last_name , department_name FROM employees e RIGHT JOIN departments d
ON e.department_id = d.department_id WHERE e.department_id is null
-- 反内连接
SELECT last_name , department_name FROM employees e LEFT JOIN departments d
ON e.department_id = d.department_id WHERE d.department_id IS NULL
UNION ALL
SELECT last_name , department_name FROM employees e RIGHT JOIN departments d
ON e.department_id = d.department_id WHERE e.department_id is NULL
