题解 | 返回产品名称和每一项产品的总订单数

select
    prod_name,
    cast(sum(判断) as unsigned) orders
from
    (
        select
            prod_name,
            if (order_num is not null, 1, 0) 判断
        from
            Products pro
            left join OrderItems ori on pro.prod_id = ori.prod_id
    ) a
group by
    prod_name
order by
    prod_name asc