Question

所以我尝试使用我在查询中创建的函数，当我执行查询时它会永远运行。该功能找到客户，他的订单最大其中的产品数量。该查询将其与任何其他查询一起返回订购了相同数量产品的客户。

这是功能：

CREATE OR REPLACE FUNCTION max_orderQty ()
RETURNS bigint
AS $$
     SELECT SUM(OrderQty)
     FROM Customer,SalesOrderHeader,SalesOrderDetail
     WHERE Customer.CustomerID = SalesOrderHeader.CustomerID
     AND SalesOrderHeader.SalesOrderID = SalesOrderDetail.SalesOrderID
     GROUP BY SalesOrderHeader.CustomerID
     ORDER BY SUM(OrderQty) DESC LIMIT 1;
$$ LANGUAGE SQL;

以下是查询：

SELECT SUM(OrderQty),SalesOrderHeader.CustomerID
FROM Customer,SalesOrderHeader,SalesOrderDetail
WHERE Customer.CustomerID = SalesOrderHeader.CustomerID
AND SalesOrderHeader.SalesOrderID = SalesOrderDetail.SalesOrderID
GROUP BY SalesOrderHeader.CustomerID
HAVING SUM(OrderQty) = max_orderQty();

这也有效，它解决了同样的问题:(在220ms内）

SELECT SUM(OrderQty),SalesOrderHeader.CustomerID
FROM Customer,SalesOrderHeader,SalesOrderDetail
WHERE Customer.CustomerID = SalesOrderHeader.CustomerID
AND SalesOrderHeader.SalesOrderID = SalesOrderDetail.SalesOrderID
GROUP BY SalesOrderHeader.CustomerID
HAVING SUM(OrderQty) = (SELECT SUM(OrderQty)
                        FROM Customer,SalesOrderHeader,SalesOrderDetail
                        WHERE Customer.CustomerID = SalesOrderHeader.CustomerID
                        AND SalesOrderHeader.SalesOrderID = SalesOrderDetail.SalesOrderID
                        GROUP BY SalesOrderHeader.CustomerID
                        ORDER BY SUM(OrderQty) DESC LIMIT 1);

因此，当我尝试将其拆分为函数/查询时，它只会永远运行而且我找不到原因。我想用一个函数代替更快。那是错的吗？

非常感谢任何帮助。提前谢谢。

Answer 1

没有理由认为函数会更快。您的问题是正在为输出中的每一行调用该函数 - 并且每次都要重新计算。

您应该能够通过将函数声明为STABLE来解决此问题。默认值为VOLATILE。

您可以在documentation中了解这些细微差别。

编辑：

只需调用一次函数，就可以强制它运行得更快：

SELECT SUM(OrderQty),SalesOrderHeader.CustomerID
FROM Customer JOIN
     SalesOrderHeader
     ON Customer.CustomerID = SalesOrderHeader.CustomerID JOIN
     SalesOrderDetail
     ON SalesOrderHeader.SalesOrderID = SalesOrderDetail.SalesOrderID CROSS JOIN
     (SELECT max_orderQty() as maxoq) x
GROUP BY SalesOrderHeader.CustomerID
HAVING SUM(OrderQty) = MAX(maxoq);

PostgreSQL函数/查询无限执行

1 个答案: