SQL select語句，根據其他列計算列

Question

我試圖總結單個價格並使用邏輯折扣。

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

我收到一個錯誤：

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

編寫查詢的正確方法是什么？

Answer 1

一種解決方案是使用子查詢來計算價格，然后在外部查詢中計算稅款和總計。

這應該工作：

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