Sql server 尝试对子查询的前1项求和

下面是我的SELECT语句的一小部分：

SELECT CASE WHEN I.IsSimCheckout=1 THEN 
    SUM(DISTINCT SalePrice) ELSE SUM(SalePrice) END 
FROM InvoiceDetail TD WHERE TD.InvoiceID = D.InvoiceID

我想做的是：

SELECT CASE WHEN I.IsSimCheckout=1 THEN 
    SUM(TOP 1 SalePrice ORDER BY SalePrice) + SUM(TOP 1 SalePrice ORDER BY SalePrice DESC) ELSE SUM(SalePrice) END 
FROM InvoiceDetail TD WHERE TD.InvoiceID = D.InvoiceID

显然，我知道后一种SQL不会编译。但基本上，我想做的是，如果I.IsSimCheckout等于1，那么我想把最高售价和最低售价相加，而不是把它们相加。希望我所做的是有意义的，并且是清楚的

我正在使用SQLServer2008

SELECT
.... 
FROM InvoiceDetail TD
OUTER APPLY
(
    SELECT TOP 1 SalePrice
    FROM D(?)
    WHERE TD.InvoiceID = D.InvoiceID
    ORDER BY SalePrice ASC 
) LP
OUTER APPLY
(
    SELECT TOP 1 SalePrice
    FROM D(?)
    WHERE TD.InvoiceID = D.InvoiceID
   ORDER BY SalePrice DESC
) HP
 WHERE TD.InvoiceID = D.InvoiceID

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这是总的想法。我将为您保留SELECT语句。

您可以使用groupby按如下方式执行此操作

  select 
  case when I.IsSimCheckout=1 then max(id.SalePrice)+min(id.SalePrice)
  else sum(id.SalePrice) as result
  from Invoice I join InvoiceDetail ID on I.InvoiceID=Id.InvoiceID
  group by i.InvoiceID, id.InvoiceID, I.IsSimCheckout

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请回顾您的问题并给出明确的方式