Question

好的，所以我有两张桌子

产品：

+------------+----------------+
| product_id | name           |
+------------+----------------+
|          1 | A product here |
+------------+----------------+
|          2 | B product here |
+------------+----------------+

和卖家

+------------+----------------+------------+
| seller_id  | in_stock       | product_id |
+------------+----------------+------------+
|          1 | 1              | 1          |
+------------+----------------+------------+
|          2 | 0              | 1          |
+------------+----------------+------------+
|          2 | 0              | 2          |
+------------+----------------+------------+

我正在试图弄清楚如何只返回所有卖家都有in_stock = 0的产品。

所以在这个特定的例子中，它只返回product_id为2的产品，因为product_id有一行in_stock = 1

Answer 1

此产品的in_stock列的最大值必须为0：

SELECT 
    product_id
FROM
    sellers
GROUP BY
    product_id
HAVING
    MAX(in_stock) = 0;

所以你通过加入获得产品信息

SELECT
    *
FROM
    products
INNER JOIN (
   SELECT 
        product_id
    FROM
        sellers
    GROUP BY
        product_id
    HAVING
        MAX(in_stock) = 0
) t
ON
    products.product_id = t.product_id;

Answer 2

我会使用以下内容来说明任何卖家未出售的产品（基本上等同于没有库存），以及卖家出售但全部缺货的产品。

select product_id
  from sellers
 group by product_id
having max(in_stock) = 0
union all
select p.product_id
  from products p
  left join sellers s
    on p.product_id = s.product_id
 where s.product_id is null

根据关系表中的标志过滤所有记录

2 个答案: