如何创建 Linq2Sql 查询，计算聚合？答案

【问题标题】：How to create Linq2Sql query, calculating aggregates?如何创建 Linq2Sql 查询，计算聚合？
【发布时间】：2014-09-16 21:40:47
【问题描述】：

有什么方法可以创建 Linq2SQL 查询，会被翻译成这样：

SELECT  COUNT(*) as totalCount ,
 SUM(v.field1) AS totalfield1,
....
 SUM(v.<fieldN>) AS total<fieldN>
FROM    [dbo].[SomeTable] v

【问题讨论】：

标签： c# .net linq linq-to-sql

【解决方案1】：

你可以试试

var query = from p in SalesOrderDetails 
         group p by p.ProductID into g
          select  new
          {id =  g.Key, Count = g.Count(), Sum = g.Sum(p => p.OrderQty)};   

Console.Write(query);

但是您使用假密钥然后枚举的解决方案似乎要好得多。

var query = from p in SalesOrderDetails 
         group p by p.ProductID into g
        select  new
  {id =  g.Key, FalseKey = 1, Count = g.Count(), Sum = g.Sum(p => p.OrderQty) };

//Console.Write(query);
var result = from q in query
                  group q by q.FalseKey into c
                  select new { summation = c.Sum(q => q.Sum)};

Console.Write(result);

【讨论】：

【解决方案2】：

我找到了 DataObjects.NET 的解决方案

var query =  
    from product in Query.All<Product>()
    where product.ProductName.Contains("a")
    select new {Product = product, FakeKey = 0} into i
    group i.Product.UnitPrice by i.FakeKey into g
    select new { Count = g.Count(), Price = g.Sum() };

  var result = query.AsEnumerable().Single();

SQL：

SELECT Count_big(*)         AS [column1], 
       SUM([a].[UnitPrice]) AS [column2] 
FROM   (SELECT [b].[ProductId], 
               [b].[TypeId], 
               [b].[ProductName], 
               [b].[Seller], 
               [b].[Category.Id], 
               [b].[ProductType], 
               [b].[UnitPrice], 
               [b].[UnitsInStock], 
               [b].[UnitsOnOrder], 
               [b].[ReorderLevel], 
               [b].[QuantityPerUnit], 
               0 AS [column] 
        FROM   [dbo].[Products] [b] 
        WHERE  ( [b].[ProductName] LIKE '%a%' )) [a] 
GROUP  BY [a].[column];

【讨论】：