C# LINQ-对多个列进行分组/求和

数据是通过OleDB加载到ado.net数据集中的本地CSV文件。该表包含40多列发票明细。每行是发票中的一个单独的行项目，可以由1到n行组成

查询用于将每张发票的发票明细分组为一行，合计发票金额和到期余额

以下是我想要确定的： 是否可以在单个查询中执行此操作

    //group the invoices by invoicenumber and sum the total
//Zoho has a separate record (row) for each item in the invoice
//first select the columns we need into an anon array   
var invoiceSum =
    DSZoho.Tables["Invoices"].AsEnumerable()
    .Select (x => 
        new {  
            InvNumber = x["invoice number"],
            InvTotal = x["item price"],
            Contact = x["customer name"],
            InvDate = x["invoice date"],
            DueDate = x["due date"],
            Balance = x["balance"],
            } );
    //then group and sum
    var invoiceTotals =
        invoiceSum
        .GroupBy (s => new {s.InvNumber, s.Contact, s.InvDate, s.DueDate} )
        .Select (g => 
            new {
                InvNumber = g.Key.InvNumber,
                InvDate = g.Key.InvDate,
                DueDate = g.Key.DueDate,
                Contact = g.Key.Contact,
                InvTotal = g.Sum (x => Math.Round(Convert.ToDecimal(x.InvTotal), 2)),
                Balance = g.Sum (x => Math.Round(Convert.ToDecimal(x.Balance), 2)),
                } );

---

事实上，当您使用invoiceTotals的结果时，您只进行了一次查询。在您显示的代码中，您甚至没有对数据库进行查询

谷歌“linq延迟执行”，很漂亮；-）

但正如乌里尔所说，您可以将这些语句组合成一个linq查询：

var invoiceSum =
DSZoho.Tables["Invoices"].AsEnumerable()
.Select (x => 
    new {  
        InvNumber = x["invoice number"],
        InvTotal = x["item price"],
        Contact = x["customer name"],
        InvDate = x["invoice date"],
        DueDate = x["due date"],
        Balance = x["balance"],
        }
 )
 .GroupBy (s => new {s.InvNumber, s.Contact, s.InvDate, s.DueDate} )
 .Select (g => 
        new {
            InvNumber = g.Key.InvNumber,
            InvDate = g.Key.InvDate,
            DueDate = g.Key.DueDate,
            Contact = g.Key.Contact,
            InvTotal = g.Sum (x => Math.Round(Convert.ToDecimal(x.InvTotal), 2)),
            Balance = g.Sum (x => Math.Round(Convert.ToDecimal(x.Balance), 2)),
            } 
 );

---

您可以将GroupBy放在第一次选择之后，而无需引入invoiceTotals VariableAH的可能副本-谢谢您的帮助。”“林克延期执行”之前也没有听过这个词。我感谢你们的帮助。哇，这是我在书堆里得到的最好的答案