Question

我需要找到每个零件价格最低的供应商。

表：供应商（sid，sname，地址），部件（pid，pname，颜色），目录（sid，pid，cost）

这有效：

SELECT 
    sname, pid
FROM
    (SELECT 
        *
    FROM
        suppliers
    NATURAL JOIN catalog
    NATURAL JOIN (SELECT 
        pid, MIN(cost) AS min_cost
    FROM
        catalog
    GROUP BY (pid)) AS m
    HAVING cost = min_cost) AS n

但是当我尝试将其缩短到以下内容时，我得到一个错误，即在having子句中存在未知成本：

SELECT 
    sname, pid
FROM
    suppliers
        NATURAL JOIN
    catalog
        NATURAL JOIN
    (SELECT 
        pid, MIN(cost) AS min_cost
    FROM
        catalog
    GROUP BY (pid)) AS m
HAVING cost = min_cost

为什么不能找到成本？表格中的成本是不是因为我已经将子查询加入了目录？

修改

根据建议，我将其更改为使用INNER JOIN而不是NATURAL JOIN，但我仍然遇到同样的错误。新查询：

SELECT 
    s.sname, m.pid
FROM
    suppliers s
        INNER JOIN
    catalog c ON s.sid = c.sid
        INNER JOIN
    (SELECT 
        pid, MIN(cost) AS min_cost
    FROM
        catalog
    GROUP BY (pid)) AS m ON c.pid = m.pid
HAVING cost = min_cost

EDIT_2

问题不是JOIN，而是HAVING，实际应该是WHERE，如bbrumm的回答所示。

Answer 1

我建议像这样的查询：

SELECT
supplier.sname,
catalog.pid
FROM suppliers
INNER JOIN catalog ON suppliers.supplier_id = catalog.supplier_id 
INNER JOIN 
    (SELECT 
     pid, MIN(cost) AS min_cost
    FROM catalog
    GROUP BY (pid)) AS m
ON catalog.pid = m.pid
WHERE catalog.cost = m.min_cost;

我对您可能需要更改的列名（例如supplier_id）做了一些假设。可以说“cost = min_cost”是JOIN的一部分，所以它也可以去那里。我也没有包括表别名，因为它是最好的做法，它不是必需的。

SQL查询查找每个部件价格最低的供应商

1 个答案: