SQL99语法新特性

自然连接

SELECT employee_id, department_name
FROM employee e JOIN department d
ON e.department_id = d.department_id
AND e.manager_id = d.manager_id;

等同于

SELECT employee_id, department_name
FROM employee e NATURAL JOIN department d;

自动查询两张表中所有相同的字段，然后进行等值连接

USING

SELECT employee_id, department_name
FROM employee e JOIN department d
ON e.department_id = d.department_id;

等同于

SELECT employee_id, department_name
FROM employee e JOIN department d
USING (department_id);