SQL：如何返回一个列，该列是另一列上返回的行的集合？

我有一张公司和发票的表格。我的查询将每个公司发票的总值相加，以提供公司的“总销售额”。我想返回的是与同一查询中的其他公司相比，每个公司销售额的+/-

Select Company.name, sum(Invoice.total) as InvoiceTotal
From Company
Inner Join Invoice on Invoice.CompanyId = Company.Id
Group By Company.name

假设上述查询生成：

Company          InvoiceTotal
A                100
B                200
C                600

我希望附加列提供超过或低于InvoiceTotal列平均值的金额：

Company          InvoiceTotal    Difference
A                100             -200
B                200             -100
C                600             300

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如何在单个查询中提取该值？

如果您的数据库可以处理窗口平均值（大多数都可以），则可以使用应用于发票总额的窗口平均值函数，然后使用发票总额执行其余操作

这是SQL Server的一个示例：

;WITH Data AS
(
    SELECT
        *
    FROM
        (
        VALUES
            ('a', 50),
            ('a', 25),
            ('a', 25),

            ('b', 125),
            ('b', 75),

            ('c', 275),
            ('c', 50),
            ('c', 75),
            ('c', 200)) V(Company, Invoice)
)
SELECT
    Company = V.Company,
    Invoice = SUM(V.Invoice),
    AverageAcrossAllCompanies = AVG(SUM(V.Invoice)) OVER (),
    AverageInvoiceDifference = SUM(V.Invoice) - AVG(SUM(V.Invoice)) OVER ()
FROM
    Data AS V
GROUP BY
    V.Company

结果:

Company Invoice AverageAcrossAllCompanies   AverageInvoiceDifference
a       100     300                         -200
b       200     300                         -100
c       600     300                         300

---

假设您的数据库支持CTE

with total as (
    select avg(invoicetotal) totalsum
from table_name)
    select t.company, 
           t.invoicetotal, 
           t.invoicetotal - total.totalsum
from table_name t, total

Company INVOICETOTAL    T.INVOICETOTAL-TOTAL.TOTALSUM
A        100            -200
B        200            -100
C        600             300

---

这里有另一种方法可以得到你想要的方差

Select
    name,
    InvoiceTotal,
    InvoiceTotal - avg(InvoiceTotal) as Difference
From
    (Select Company.name, sum(Invoice.total) as InvoiceTotal
    From Company
    Inner Join Invoice on Invoice.CompanyId = Company.Id
    Group By Company.name)
group by name, InvoiceTotal

---

可通过以下查询获得结果：

Select Company.company, sum(Invoice.total) as InvoiceTotal, (SELECT AVG(Invoice.total) FROM Invoice) AS InvoiceAvg,(SELECT AVG(Invoice.total) FROM Invoice) -sum(Invoice.total) AS Difference
From Company
Inner Join Invoice on Invoice.CompanyId = Company.Id
Group By Company.company

---

您正在使用哪个数据库管理系统？@Tanner Snowflake