Linq to Sql用于对一组数据进行计数和平均（无分组）

Question

我想执行一个Linq to Sql语句来捕获（过滤的）数据集中的计数和平均值。我有什么工作，但它需要对数据库进行两次查询，以便在一个查询中可以进行查询。

有趣的是，当我使用group by子句时，可以发出一个查询。

例如：

select count(*), avg(duration) from events 

我的LINQ看起来是这样的：

var x = from e in db.events 
     select e; 
x = from i in x 
    where i.NAME == "foo" 
    select i; 

return new { 
    count = x.Count(), 
    avgDuration = x.Average(e => e.Duration) 
    }; 

与该代码，我得到两个查询：

SELECT AVG([t0].[DURATION]) AS [value] FROM [dbo].[EVENTS] AS [t0] 

和

SELECT COUNT(*) AS [value] FROM [dbo].[EVENTS] AS [t0] 

还有别的办法吗？

Answer 1

我能得到的最好的是一个嵌套子查询：

var x = from e in db.events 
     group e by 1 into grp 
     select new { 
      count = grp.Count(), 
      avgDuration = grp.Average(x => x.Duration) } 

根据LINQPad，这将输出的SQL：

DECLARE @p0 Int = 1 

SELECT COUNT(*) AS [count], AVG([t1].[Amount]) AS [avgDuration] 
FROM (
    SELECT @p0 AS [value], [t0].[Duration] 
    FROM Events AS [t0] 
    ) AS [t1] 
GROUP BY [t1].[value]