-- rel Q cost 65%
SELECT tblAfdelingen.Afd_ID, tblAfdelingen.AfdGUID, tblAfdelingen.AfdNaam,
    (SELECT count(*) FROM tblMessageKoppel WHERE Mk_Afd_ID=Afd_ID AND (MkInBehandelingBij is null OR MkInBehandelingBij=0)) as cntMsg
FROM tblAfdelingen
WHERE Afd_ID IN
    (SELECT Gek_Afd_ID FROM tblGebruikersAfdelingKoppel WHERE Gek_Ge_ID=@userId)
ORDER BY AfdNaam

-- rel Q cost 35% -- by EF
SELECT
    [Project4].[Afd_ID] AS [Afd_ID],
    [Project4].[AfdNaam] AS [AfdNaam],
    [Project4].[C1] AS [C1]
    FROM ( SELECT
        [Project3].[Afd_ID] AS [Afd_ID],
        [Project3].[AfdNaam] AS [AfdNaam],
        [Project3].[C1] AS [C1]
        FROM ( SELECT
            [Project2].[Afd_ID] AS [Afd_ID],
            [Project2].[AfdNaam] AS [AfdNaam],
            (SELECT
                COUNT(1) AS [A1]
                FROM [dbo].[tblMessageKoppel] AS [Extent3]
                WHERE ([Project2].[Afd_ID] = [Extent3].[Mk_Afd_ID]) AND (([Extent3].[MkInBehandelingBij] IS NULL) OR ((0 = [Extent3].[MkInBehandelingBij]) AND ([Extent3].[MkInBehandelingBij] IS NOT NULL)))) AS [C1]
            FROM ( SELECT
                [Extent1].[Afd_ID] AS [Afd_ID],
                [Extent1].[AfdNaam] AS [AfdNaam]
                FROM [dbo].[tblAfdelingen] AS [Extent1]
                WHERE  EXISTS (SELECT
                    1 AS [C1]
                    FROM [dbo].[tblGebruikersAfdelingKoppel] AS [Extent2]
                    WHERE (3 = [Extent2].[Gek_Ab_ID]) AND ([Extent2].[Gek_Ab_ID] IS NOT NULL) AND ((([Extent2].[Gek_Ge_ID] = @p__linq__0) AND ( NOT ([Extent2].[Gek_Ge_ID] IS NULL OR @p__linq__0 IS NULL))) OR (([Extent2].[Gek_Ge_ID] IS NULL) AND (@p__linq__0 IS NULL))) AND ([Extent2].[Gek_Afd_ID] = [Extent1].[Afd_ID]) AND ([Extent2].[Gek_Afd_ID] IS NOT NULL)
                )
            )  AS [Project2]
        )  AS [Project3]
    )  AS [Project4]
    ORDER BY [Project4].[AfdNaam] ASC