PostgreSQL函数/查询无限执行

Question

因此，我尝试使用在查询中创建的函数，并在执行查询时使其永远运行。 该功能查找客户其订单中产品数量最多的客户。 该查询将其与订购了相同数量产品的任何其他客户一起返回。

这是函数：

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;  

这是查询：

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，并且解决了同一件事：（220ms）

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，它会永远运行，而我找不到原因。而且我认为使用函数会更快，这是错误的吗？

任何帮助都非常感谢。 提前致谢。

Answer 1

没有理由认为某个功能会更快。 您的问题是正在为输出中的每一行调用该函数-并且每次都在重新进行计算。

您应该可以通过将函数声明为STABLE来解决此问题； 默认值为VOLATILE 。

您可以在文档中了解这些细微差别。

编辑：

您可以通过仅调用一次函数来使其运行更快：

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);