SQL select语句，根据其他列计算列答案

【问题标题】：SQL select statement, calculating columns based on other columnsSQL select语句，根据其他列计算列
【发布时间】：2016-04-12 18:56:44
【问题描述】：

我正在尝试总结各个价格并使用折扣逻辑。

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？

【问题讨论】：

您不能在select 子句中重复使用别名。
所以我需要将整个逻辑子句复制粘贴到选择的每个部分吗？我需要做一个中间视图来保持价格，然后再做税收和总计吗？
您可以复制/粘贴 select 子句中的逻辑

标签： mysql sql sql-function

【解决方案1】：

一种解决方案是使用子查询计算价格，然后在外部查询中计算税金和总计。

这应该可行：

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

【讨论】：