select 表关系

Question

我需要帮助。我有 3 个这样的 table：

product
    * id
    - name

supplier
    * id
    - name
    - active

product_supplier
    * id_product
    * id_supplier

最后table向供应商列出产品。

我需要的是建立一个查询，returns 我只有活跃的供应商，但仍然与特定产品无关。

谢谢！！

Answer 1

用子查询试试这个：

SELECT *
FROM supplier
WHERE active = 'Y'
AND id NOT IN (SELECT DISTINCT id_supplier
               FROM product_supplier)

Answer 2

这是你的问题："What I need is to build a query that returns me only active suppliers and still are not related to specific product."

您正在寻找没有特定产品的活跃供应商。

select s.id
from product_supplier ps join
     supplier s
     on ps.id_supplier = s.id
where s.active = 1
group by s.id
having sum(case when ps.id_product = XX then 1 else 0 end) > 0;

您也可以使用 not exists:

select s.id
from supplier s
where s.active = 1 and
      not exists (select 1
                  from product_supplier ps
                  where ps.id_supplier = s.id and
                        ps.id_product = XX
                 )

而且，您可以使用 left join:

select s.*
from supplier s left join
     product_supplier ps
     on ps.id_supplier = s.id and ps.id_product = XX
where s.active = 1 and ps.id_supplier is null;

这似乎是 SQL 中最自然的表达方式。

Answer 3

非常感谢...它适用于此。

SELECT * 
FROM supplier s
WHERE NOT 
EXISTS (
SELECT * 
FROM product_supplier ps
WHERE s.id = ps.id_supplier
AND ps.id_product =5
)
AND s.active =1

select 表关系

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