Linq to SQL:如何在没有分组的情况下聚合？

Question

我正在搜索与此查询等效的Linq-to-SQL:

SELECT
  [cnt]=COUNT(*),
  [colB]=SUM(colB),
  [colC]=SUM(colC),
  [colD]=SUM(colD)
FROM myTable

这是一个没有分组的聚合.我似乎无法找到任何方法,只发出四个单独的查询(一个Count和三个Sum).有任何想法吗？

Answer 1

这是我发现似乎你仍然需要做一个组...可以只使用常量:

var orderTotals =
    from ord in dc.Orders
    group ord by 1 into og
    select new
    {
        prop1 = og.Sum(item=> item.Col1),
        prop2 = og.Sum(item => item.Col2),
        prop3 = og.Count(item => item.Col3)
    };

这会生成以下SQL,这不是最佳的,但可以工作:

SELECT SUM([Col1]) as [prop1], SUM([Col2]) as [prop2], COUNT(*) AS [prop3]
FROM (
    SELECT 1 AS [value], [t0].[Col1], [t0].[Col2], [t0].[Col3]
    FROM [table] AS [t0]
    ) AS [t1]
GROUP BY [t1].[value]

Answer 2

您可以使用Lambda表达式执行相同的查询,如下所示:

  var orderTotals = db.Orders
                      .GroupBy( i => 1)
                      .Select( g => new
                      {
                           cnt = g.Count(), 
                           ScolB = g.Sum(item => item.ColB), 
                           ScolC = g.Sum(item => item.ColC) 
                      });