PostgreSQL函數/查詢無限執行

Question

因此，我嘗試使用在查詢中創建的函數，並在執行查詢時使其永遠運行。 該功能查找客戶其訂單中產品數量最多的客戶。 該查詢將其與訂購了相同數量產品的任何其他客戶一起返回。

這是函數：

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;  

這是查詢：

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();

這也有效，並且解決了同一件事：（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，當我嘗試將其拆分為函數/查詢時，它會永遠運行，而我找不到原因。而且我認為使用函數會更快，這是錯誤的嗎？

任何幫助都非常感謝。 提前致謝。

Answer 1

沒有理由認為某個功能會更快。 您的問題是正在為輸出中的每一行調用該函數-並且每次都在重新進行計算。

您應該可以通過將函數聲明為STABLE來解決此問題； 默認值為VOLATILE 。

您可以在文檔中了解這些細微差別。

編輯：

您可以通過僅調用一次函數來使其運行更快：

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);