SQL视图中的表达式

我不熟悉SQL视图，所以请温柔一点

我有以下SQL视图：

SELECT        dbo.product.name AS [Product Name], 
              ROUND(CASE [vat] WHEN 1 THEN [packcost] * 1.2 ELSE [packcost] END, 2) AS [Pack Cost],            
              ROUND(CASE [vat] WHEN 1 THEN ([packcost] * 1.2) / [units] ELSE [packcost] / [units] END, 2) AS [Unit Cost],
              dbo.purchase.unitsaleprice * dbo.product.units AS [ Pack Sale Price], dbo.purchase.unitsaleprice AS [Unit Sale Price],
              dbo.product.units * (dbo.purchase.unitsaleprice - ROUND(CASE [vat] WHEN 1 THEN ([packcost] * 1.2) / [units] ELSE [packcost] / [units] END, 2)) AS [Pack Profit], 
              dbo.purchase.unitsaleprice - ROUND(CASE [vat] WHEN 1 THEN ([packcost] * 1.2) / [units] ELSE [packcost] / [units] END, 2) AS [Unit Profit] 
           FROM dbo.product INNER JOIN
              dbo.purchase ON dbo.product.id = dbo.purchase.productID

但它似乎效率低下，因为我重写了很多

例如，我想定义[Pack Cost]列：

ROUND(CASE [vat] WHEN 1 THEN [packcost] * 1.2 ELSE [packcost] END, 2) AS [Pack Cost]

用于其他地方，而不是重写它

e、 g因此我可以使用：

[Pack Cost] / [Units]

要定义单位成本而不是：

ROUND(CASE [vat] WHEN 1 THEN ([packcost] * 1.2) / [units] ELSE [packcost] / [units] END, 2) AS [Unit Cost]

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但是，我不确定我是否得到了正确的结果，或者这样做是否合适。

您可以创建一个标量函数来为您实现该逻辑。然后您可以在视图中调用该函数。

使用计算逻辑创建一个中间视图。例如，将其称为ProductEx。此视图可以计算PackCost列并为其命名。然后根据视图ProductEx而不是表Product编写所有其他视图。

我的经验是，与执行简单计算的成本相比，获取行的“成本”非常大，我根本不关心它。 我想说可读性和/或抽象性更值得关注

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另外，您的dbms可能已经在幕后执行了这些优化，但您应该对这两种方法进行测量以确保其正确性。

您可以在子查询中定义它

SELECT p.name AS [Product Name], 
 P.[Pack Cost] AS [Pack Cost], 
 Round(P.[Pack Cost] / [units],2) AS [Unit Cost],
 dbo.purchase.unitsaleprice * p.units AS [ Pack Sale Price], dbo.purchase.unitsaleprice AS [Unit Sale Price],
 p.units * (dbo.purchase.unitsaleprice - Round(P.[Pack Cost] / [units],2)) AS [Pack Profit], 
 dbo.purchase.unitsaleprice - Round(P.[Pack Cost] / [units],2) AS [Unit Profit] 
FROM 
 (SELECT *, [Pack Cost] = ROUND(CASE [vat] WHEN 1 THEN [packcost] * 1.2 ELSE [packcost] END, 2) FROM dbo.product) p
INNER JOIN dbo.purchase ON p.id = dbo.purchase.productID

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或者，如果要经常进行计算，可以向原始表中添加一个计算字段，称为PackCost。然后，caclis只在数据输入时执行，或者不在每次查询时进行更改。

创建一个新的用户定义标量值函数，如下所示：

CREATE FUNCTION [dbo].[GetPackCost] 
(
    @vat int
    ,@packcost decimal
)
RETURNS decimal
AS
BEGIN
    DECLARE @packcost_calculated decimal

    SELECT @packcost_calculated = ROUND(CASE @vat WHEN 1 THEN @packcost * 1.2 ELSE @packcost END, 2) 

    RETURN @packcost_calculated

END

GO

SELECT        dbo.product.name AS [Product Name], 
              dbo.GetPackCost([vat],[packcost]) AS [Pack Cost],            
              dbo.GetPackCost([vat],[packcost]) / [units] AS [Unit Cost],
              dbo.purchase.unitsaleprice * dbo.product.units AS [ Pack Sale Price], dbo.purchase.unitsaleprice AS [Unit Sale Price],
              dbo.product.units * (dbo.purchase.unitsaleprice - ROUND(CASE [vat] WHEN 1 THEN ([packcost] * 1.2) / [units] ELSE [packcost] / [units] END, 2)) AS [Pack Profit], 
              dbo.purchase.unitsaleprice - ROUND(CASE [vat] WHEN 1 THEN ([packcost] * 1.2) / [units] ELSE [packcost] / [units] END, 2) AS [Unit Profit] 
           FROM dbo.product INNER JOIN
              dbo.purchase ON dbo.product.id = dbo.purchase.productID

在您的查询中，您将选择如下：

CREATE FUNCTION [dbo].[GetPackCost] 
(
    @vat int
    ,@packcost decimal
)
RETURNS decimal
AS
BEGIN
    DECLARE @packcost_calculated decimal

    SELECT @packcost_calculated = ROUND(CASE @vat WHEN 1 THEN @packcost * 1.2 ELSE @packcost END, 2) 

    RETURN @packcost_calculated

END

GO

SELECT        dbo.product.name AS [Product Name], 
              dbo.GetPackCost([vat],[packcost]) AS [Pack Cost],            
              dbo.GetPackCost([vat],[packcost]) / [units] AS [Unit Cost],
              dbo.purchase.unitsaleprice * dbo.product.units AS [ Pack Sale Price], dbo.purchase.unitsaleprice AS [Unit Sale Price],
              dbo.product.units * (dbo.purchase.unitsaleprice - ROUND(CASE [vat] WHEN 1 THEN ([packcost] * 1.2) / [units] ELSE [packcost] / [units] END, 2)) AS [Pack Profit], 
              dbo.purchase.unitsaleprice - ROUND(CASE [vat] WHEN 1 THEN ([packcost] * 1.2) / [units] ELSE [packcost] / [units] END, 2) AS [Unit Profit] 
           FROM dbo.product INNER JOIN
              dbo.purchase ON dbo.product.id = dbo.purchase.productID

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对不起，我麻木了，你能再给我一些建议吗？我会创建一个返回[Pack Cost]的函数吗？