SQL查询 - 查询需要一些帮助

Question

我附上了ER图。这很简单。产品，产品类型，制造商及其协会。

查询需要做的是返回制造商的姓氏，以及他们生产的产品的产品名称，条件是这些制造商生产了至少两种不同类型的产品。

非常感谢回复。他们非常有用和有教育意义。我真的很感激。

Answer 1

这样做的一种方法是使用where子句中的子选择来过滤您的选择。我这样做的速度非常快，只是为了证明：

select * from manufacturer m 
inner join manufacturer_has_product mhp
    on m.manufacturer_id = m.manufacturer_id
inner join product p
    on mhp.product_id = p.product_id
where m.manufacturer_id in (
    select m.manufacturer_id
    from manufacturer m
    inner join manufacturer_has_product mhp
        on m.manufacturer_id = m.manufacturer_id
    inner join product p
        on mhp.product_id = p.product_id
    inner join productType_has_product pthp
        on pt.product_product_id = p.product_id
    inner join productType pt
        on pt.productType_type_id = pt.type_id
    group by m.manufacturer_id
    having count(pt.type_id) > 1
    )

Answer 2

很难看到没有任何数据，但这是一个镜头。

select p.Name, m.last_name from Product p
inner join manufacturer m on m.manufacturer_id = p.product_id
inner join productType pT on p.product_id = pT.type_id 
where COUNT(distinct pT.type_id) >= 2 
group by m.manufacturer_id 

Answer 3

灵感来自@ Eric的答案，未经过测试，评论中的解释......

SELECT tmp.last_name, p.name -- <- compose the final select 
FROM
-- sub-select the underlying manufacturers (id + last_name):
(
    -- distinct ... or join deeper
    SELECT COUNT (DISTINCT php.productType_type_id), m.manufacturer_id, m.last_name
    FROM manufacturer m
    JOIN manufacturer_has_product mhp
    ON (mhp.manufacturer_manufacturer_id = m.manufacturer_id)
    JOIN Product p
    ON (p.product_id = mhp.Product_product_id)
    --- until "php" is enough, but needs distinct
    JOIN productType_has_product php
    ON (php.Product_product_id = p.product_id)
    -- obligatory:
    GROUP BY m.manufacturer_id, m.last_name
    -- (aggregated) filter condition: 
    HAVING COUNT (DISTINCT php.productType_type_id) > 1
) tmp -- an alias for the sub-select
-- join for the final result:
JOIN manufacturer_has_product mhp
-- on TMP.manufacturer_id!
ON (mhp.manufacturer_manufacturer_id = tmp.manufacturer_id) 
JOIN Product p ON (p.product_id = mhp.Product_product_id)