SQL select语句，根据其他列计算列

Question

我试图总结单个价格并使用逻辑折扣。

SELECT O.OrderID, 
    if(C.IsClubMember & OrderNumber % 10 = 0, 0.5 * Sum(I.ItemPrice), Sum(I.ItemPrice)) as Price, 
    0.07*Price as Tax, Price + Tax as Total
FROM Orders as O JOIN ItemPriceView as I 
    ON O.OrderID = I.OrderID JOIN Customer as C 
    ON O.CustomerID = C.CustomerID
GROUP BY OrderID

我收到一个错误：

Error Code: 1054. Unknown column 'Price' in 'field list'

编写查询的正确方法是什么？

Answer 1

一种解决方案是使用子查询来计算价格，然后在外部查询中计算税款和总计。

这应该工作：

SELECT OrderID, Price, 0.07*Price as Tax, 1.07*Price as Total
FROM
(
SELECT O.OrderID as OrderID, 
    if(C.IsClubMember & OrderNumber % 10 = 0, 0.5 * Sum(I.ItemPrice),Sum(I.ItemPrice)) as Price
FROM Orders as O JOIN ItemPriceView as I 
    ON O.OrderID = I.OrderID JOIN Customer as C 
    ON O.CustomerID = C.CustomerID
GROUP BY OrderID
) as sub_query