1.举例以消费者ID为主键连接订单表和客户表
    SELECT
    o.order_id,
    c.first_name
    FROM orders o
    JOIN customers c
    ON o.customer_id = c.customer_id
    考虑如何使用USING子句来简化查询
    SELECT
    o.order_id,
    c.first_name,
    sh.name as shipper
    FROM orders o
    JOIN customers c
    USING (customer_id)
    LEFT JOIN shipeers sh
    USING (shipper_id)

    2.对应两表中使用双主键来确定数据
    SELECT
    FROM order_items oi
    JOIN order_items_notes oin
    ON oi.order_id = oin.order_id AND
    oi.product_id = oin.product_id
    USING简化
    SELECT
    FROM order_items oi
    JOIN order_items_notes oin
    USING (order_id, product_id)

    练习：
    连接payments和clients两张表后再连接付款方式
    SELECT *
    FORM payments p
    JOIN clients USING (client_id)
    JOIN payment_methods pm
    ON p.payment_method = pm.payment_method_id