如何让EF6生成包含多个聚合列的高效SQL？

我正在尝试使用Entity Framework（v6.1.3）为具有多个聚合的查询生成高效的SQL。

这是一个简化的例子。

表：

CREATE TABLE [dbo].[CaseAttorney]( [CaseAttorneyID] [int] IDENTITY(1,1) NOT NULL, [CaseNumber] [varchar](30) NOT NULL, [AttorneyID] [int] NOT NULL, [DateAssigned] [datetime] NULL, [DateUnassigned] [datetime] NULL, CONSTRAINT [PK_CaseAttorney] PRIMARY KEY CLUSTERED ( [CaseAttorneyID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] 

C＃：

 using (var cx = new DATA()) { var startDate = DateTime.Parse("1/1/2014"); var endDate = startDate.AddDays(1); cx.Database.Log = Console.WriteLine; var res = cx.CaseAttorneys. GroupBy(o => new { AttorneyID = o.AttorneyID }).Select(g => new { AttorneyID = g.Key.AttorneyID, ActiveStart = g.Sum(item => (item.DateAssigned = startDate) ? 1 : 0)), Assigned = g.Sum(item => (item.DateAssigned >= startDate && item.DateAssigned <= endDate) ? 1 : 0) }).ToArray(); } 

我得到一个包含多个嵌套表的非常低效的查询，而不是使用单个GROUP BY生成查询。 COUNT和SUM都会发生这种情况：

 SELECT [Project3].[AttorneyID] AS [AttorneyID], [Project3].[C1] AS [C1], [Project3].[C2] AS [C2] FROM ( SELECT [Project2].[AttorneyID] AS [AttorneyID], [Project2].[C1] AS [C1], (SELECT SUM([Filter2].[A1]) AS [A1] FROM ( SELECT CASE WHEN (([Extent3].[DateAssigned] >= @p__linq__2) AND ([Extent3].[DateAssigned] <= @p__linq__3)) THEN 1 ELSE 0 END AS [A1] FROM [dbo].[CaseAttorney] AS [Extent3] WHERE [Project2].[AttorneyID] = [Extent3].[AttorneyID] ) AS [Filter2]) AS [C2] FROM ( SELECT [Distinct1].[AttorneyID] AS [AttorneyID], (SELECT SUM([Filter1].[A1]) AS [A1] FROM ( SELECT CASE WHEN (([Extent2].[DateAssigned] = @p__linq__1))) THEN 1 ELSE 0 END AS [A1] FROM [dbo].[CaseAttorney] AS [Extent2] WHERE [Distinct1].[AttorneyID] = [Extent2].[AttorneyID] ) AS [Filter1]) AS [C1] FROM ( SELECT DISTINCT [Extent1].[AttorneyID] AS [AttorneyID] FROM [dbo].[CaseAttorney] AS [Extent1] ) AS [Distinct1] ) AS [Project2] ) AS [Project3] 

如果不能一遍又一遍地敲击相同的表格，嵌入本身并不会太糟糕。 添加的聚合列越多，此问题就越严重。

我这里没有发现任何类似的问题，所以我确定我做错了什么。

当我想返回多个聚合列时，让entity framework生成有效投影的正确方法是什么？

Answer 1

Count(predicate) （实际上涉及谓词的任何函数）似乎对生成的SQL查询产生了影响。

但是，条件Sum （即Sum(predicate ? 1 : 0) ）没有这样的影响，所以以下将做你想要的：

更新：事实certificate， Sum技巧是必要的，但是当谓词使用像你的情况一样的变量时，它是不够的。 它很可能是EF错误，因为使用不同的GroupBy重载没有帮助，除非你在进行GroupBy 之前包含一个包含条件表达式的临时投影。

所以（最后）以下查询

 db.CaseAttorneys.Select(item => new { Item = item, ActiveStart = item.DateAssigned < startDate && (item.DateUnassigned == null || item.DateUnassigned >= startDate) ? 1 : 0, Assigned = item.DateAssigned >= startDate && item.DateAssigned <= endDate ? 1 : 0 }) .GroupBy(o => new { AttorneyID = o.Item.AttorneyID }) .Select(g => new { AttorneyID = g.Key.AttorneyID, ActiveStart = g.Sum(item => item.ActiveStart), Assigned = g.Sum(item => item.Assigned) }).ToArray(); 

产生了所需的SQL

 SELECT [GroupBy1].[K1] AS [AttorneyID], [GroupBy1].[A1] AS [C1], [GroupBy1].[A2] AS [C2] FROM ( SELECT [Extent1].[K1] AS [K1], SUM([Extent1].[A1]) AS [A1], SUM([Extent1].[A2]) AS [A2] FROM ( SELECT [Extent1].[AttorneyID] AS [K1], CASE WHEN (([Extent1].[DateAssigned] < @p__linq__0) AND (([Extent1].[DateUnassigned] IS NULL) OR ([Extent1].[DateUnassigned] >= @p__linq__1))) THEN 1 ELSE 0 END AS [A1], CASE WHEN (([Extent1].[DateAssigned] >= @p__linq__2) AND ([Extent1].[DateAssigned] <= @p__linq__3)) THEN 1 ELSE 0 END AS [A2] FROM [dbo].[CaseAttorneys] AS [Extent1] ) AS [Extent1] GROUP BY [K1] ) AS [GroupBy1]