我计算字段的逻辑有什么问题（试图计算百分比）？

Question

我用来计算百分比的 TSQL 显然搞砸了；这是我的存储过程逻辑的一部分：

. . .
AVG(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END) 
Week1Price,
    AVG(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.Price ELSE 0 END) 
Week2Price,
    AVG(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.Price ELSE 0 END) 
 -
    AVG(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END) 
PriceVariance,
    AVG(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.Price ELSE 0 END) 
 -
    AVG(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END) 
    / 
NULLIF(AVG(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END),0) 
PercentageOfPriceVariance
. . .

我想用 PercentageOfPriceVariance 做的是：

(Week2Price - Week1Price) / Week1Price

例如，如果 Week2Price 为 3.38，Week1Price 为 20.27，则 (Week2Price - Week1Price) 应为 -16.89；然后 (-16.89) 除以 3.38 应该是 -4.99.

不过请注意，我得到的结果与那个结果大不相同（请参阅第 3 行，其中 % 为 2.38）：

我计算字段的逻辑有什么问题？

Answer 1

括号应该适用于第一个集合，即 (Week2Price - Week1Price) 否则除法运算 Week1Price / Week2Price 将首先执行减法运算。这就是结果与您的预期不同的原因。

看例子：

SELECT (3.38 - 20.27) / NULLIF(3.38, 0) -- result -4.997041
SELECT 3.38 - 20.27 / NULLIF(3.38, 0)   -- result -2.617041

所以你需要为第一组应用括号就可以解决问题。

注意： 在您的实际代码中，除数部分仅包含 WeeK1Price，但在 post 中您提到数据需要除以 Week2Price。

当前您的代码 returns 由于错误的除数导致数据错误。

SELECT 3.38 - 20.27 / NULLIF(20.27, 0)  -- result 2.3800000

所以你的实际代码应该是：

(
 AVG(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.Price ELSE 0 END) 
-
 AVG(CASE WHEN Ind.InvoiceDate BETWEEN @BegDate AND @Week1End THEN Ind.Price ELSE 0 END)
) 
/ 
NULLIF(AVG(CASE WHEN Ind.InvoiceDate BETWEEN @Week2Begin AND @EndDate THEN Ind.Price ELSE 0 END), 0) 
PercentageOfPriceVariance

我计算字段的逻辑有什么问题（试图计算百分比）？

What is wrong with my calculated field's logic (trying to compute percentage)?

tsql

sql-server

math

stored-procedures

percentage