Question

我必须显示包含来自同一生产商的至少三种产品的订单但它会返回所有订单代码而不是我要求的订单代码。显然我的代码是错误的。任何想法如何解决它？我应该尝试不同于计数的东西吗？

create view Orders as
select order_code, Consists.product_code, Offer.producer_code
from Consists, Producers, Offer, Product
where Consists.product_code = Product.product_code 
      and Product.product_code = Offer.product_code 
      and Offer.producer_code = Producers.producer_code


select order_code
from Order_a
where exists   (select Orders.order_code, Orders.producer_code
        from Orders, Offer
            where Orders.product_code = Offer.product_code 
                and Orders.producer_code = Offer.producer_code
        group by Orders.producer_code, Orders.product_code
        having count(Offer.product_code) >=3 )

Answer 1

您需要将内部查询与外部查询相关联。子查询还需要通过order_code和producer_code：

固定到组

select order_code
from Order_a
where order_code in (select Orders.order_code
                     from Orders join
                          Offer
                          on Orders.product_code = Offer.product_code and
                             Orders.producer_code = Offer.producer_code
                     group by Orders.order_code, Orders.producer_code
                     having count(Offer.product_code) >=3
                    );

我也想知道条件应该是having count(distinct offer.product_code) >= 3)。

您的查询返回所有行，因为子查询始终生成结果，因此exists为真。

使count（）替代至少3

1 个答案: