1.选择客户中所有没有填写手机号的客户
    SELECT
    FROM customers
    WHERE phone *IS NULL

    2.选择客户中所有填写手机号的客户
    SELECT
    FROM customers
    WHERE phone *IS NOT NULL

    3.筛选出所有还没有被运输的订单
    SELECT
    FROM sql_store.orders
    WHERE shipped_date *IS NULL