在组内进行Transact SQL计算

Question

我想计算群组内的权重。假设我有一个这样的表和一个组变量，我想计算权重列，它是产品值，超过该组中所有产品值的总和。怎么办呢？

数据示例：

我想从这张桌子开始：

到此表：

这意味着权重列不存在。目标是创建一个包含所有原始列的新表以及一个名为weight的新列。

重量计算示例：对于第5行B组产品x，重量计算为重量= 10/40。

Answer 1

您可以使用窗口功能来实现此目的。这是一个例子：

SELECT
    1.0 / (SUM([Value]) OVER (PARTITION BY [Group])) * [Value] AS [Weight]
FROM [YourTable]

我建议您在现有表格的基础上创建一个视图（当然，这取决于您的需求）。您可以像这样创建视图：

CREATE VIEW [YourView] AS
SELECT
    [Group],
    Product,
    [Value],
    CASE 
        WHEN (SUM([Value]) OVER (PARTITION BY [Group])) = 0 THEN 0 
        ELSE 1.0 / (SUM([Value]) OVER (PARTITION BY [Group])) * [Value] END AS [Weight] 
FROM [YourTable]

Answer 2

SELECT [group], SUM(weight)
FROM table
GROUP BY [group]

在回复您的评论时 - 您可以创建一个视图，当您查询它时会动态计算重量：

CREATE VIEW [dbo].[GroupWeights]
AS
SELECT [group], SUM(weight)
FROM table
GROUP BY [group]

回答您问题中最近的修改：

CREATE VIEW ProductWeights
AS
SELECT [p.group], product, value, (value / (SELECT SUM(value) FROM Products WHERE [group] = [p.group] GROUP BY [group])) AS [weight]
FROM Products AS p

Answer 3

您可以使用SELECT INTO创建新表，使用分区SUM来按组获取总和，如下所示：

Select [Group], Product, [Value], 
   [Weight] = ([Value]*1.0)/SUM([Value]) over(Partition by [Group])
   INTO NewTable from YourTable