Get max & min from Entity Framework, in one query and with best query possible

问题

I'm aware of this question, but what I would like to do is obtain something close to this generated SQL:

select MAX(Column), MIN(Column) from Table WHERE Id = 1

When I try this:

var query = from d in db.Table
            where d.Id == 1
            select new
            {
                min = db.Table.Max(s => s.Column),
                max = db.Table.Min(s => s.Column)
            };

The generated sql looks like this:

SELECT 
    [Extent1].[Id] AS [Id], 
    [GroupBy1].[A1] AS [C1], 
    [GroupBy2].[A1] AS [C2]
    FROM   [dbo].[Table] AS [Extent1]
    CROSS JOIN  (SELECT 
        MAX([Extent2].[Column]) AS [A1]
        FROM [dbo].[Table] AS [Extent2] ) AS [GroupBy1]
    CROSS JOIN  (SELECT 
        MIN([Extent3].[Column]) AS [A1]
        FROM [dbo].[Table] AS [Extent3] ) AS [GroupBy2]
    WHERE ([Extent1].[Id] = 1) AND (1 IS NOT NULL)

I also tried this:

var query = from d in db.Table
           where d.Id == 1
           group d by d.Id into grp
           let min = grp.Min(s => s.Column)
           let max = grp.Max(s => s.Column)
           select new { min, max };

Which gives this:

SELECT 
    [Project2].[Id] AS [Id], 
    [Project2].[C1] AS [C1], 
    [Project2].[C2] AS [C2]
    FROM ( SELECT 
        [Project1].[C1] AS [C1], 
        [Project1].[Id] AS [Id], 
        (SELECT 
            MAX([Extent2].[Column]) AS [A1]
            FROM [dbo].[Table] AS [Extent2]
            WHERE ([Extent2].[Id] = 1) AND (1 IS NOT NULL) AND ([Project1].[Id] = [Extent2].[Id])) AS [C2]
        FROM ( SELECT 
            [GroupBy1].[A1] AS [C1], 
            [GroupBy1].[K1] AS [Id]
            FROM ( SELECT 
                [Extent1].[Id] AS [K1], 
                MIN([Extent1].[Column]) AS [A1]
                FROM [dbo].[Table] AS [Extent1]
                WHERE ([Extent1].[Id] = 16) AND (16 IS NOT NULL)
                GROUP BY [Extent1].[Id]
            )  AS [GroupBy1]
        )  AS [Project1]
    )  AS [Project2]

They both work, and the performance hit is probably negligible, so it's mostly aesthetic:
The two generated queries both hurt my eyes.

回答1:

Try removing the let statements - the below produces expected results:

var q = from d in db.Table
        where d.Id == 1
        group d by d.Id into g
        select new
        {
            Id = g.Key, // shown for illustrative purposes
            ColumnMin = g.Min( gi => gi.Column ),
            ColumnMax = g.Max( gi => gi.Column )
        };

var result = q.SingleOrDefault();

Resulting SQL:

SELECT 
    [GroupBy1].[K1] AS [Id],
    [GroupBy1].[A1] AS [C1], 
    [GroupBy1].[A2] AS [C2]
    FROM ( SELECT 
        [Extent1].[Id] AS [K1], 
        MIN([Extent1].[Column]) AS [A1], 
        MAX([Extent1].[Column]) AS [A2]
        FROM [dbo].[Table] AS [Extent1]
        WHERE 1 = [Extent1].[Id]
        GROUP BY [Extent1].[Id]
    )  AS [GroupBy1]

回答2:

var query = from d in db.Table
            where d.Id == 1
            select
            {     
                d.Max(t =>t.yourColName),  
                d.Min(t =>t.yourColName)  
            };

来源：https://stackoverflow.com/questions/27376637/get-max-min-from-entity-framework-in-one-query-and-with-best-query-possible

标签

linq

entity-framework

generated-sql