Помогите ускорить выполнение запроса

                SELECT Clients.Id_Client, 
                dbo.udf_ONI([Organization],[clients].[Name],[Initials]) AS [To], 
                Zip, 
                LTrim(RTrim(isnull([Region],'') + ' ' + isnull([clients].[Address],'') + ' ' + isnull([Flat],''))) AS Location 
                FROM ((Clients INNER JOIN Forms ON Clients.Id_Client = Forms.Id_Client) INNER JOIN Orders ON Forms.Id_Form = Orders.Id_Form) INNER JOIN Products ON Orders.Id_Product = Products.Id_Product 
                WHERE Products.Id_Customer=4 AND Clients.[Name]='Петров' 
                GROUP BY Clients.Id_Client, dbo.udf_ONI([Organization],[clients].[Name],[Initials]), Zip, LTrim(RTrim(isnull([Region],'') + ' ' + isnull([clients].[Address],'') + ' ' + isnull([Flat],'')))

--конвертор и округлятор денег и веса к виду 25458.456 к 25 458.456
--включая 0.456 к 0.456, а не к .456
--и 0.4565674 к 0.456
--на точности округления пока не заморачивался, потому как нужно примерно
 
CREATE FUNCTION udf_Conv (@sum as money, @type as bit)  
RETURNS varchar(255)
AS  
BEGIN 
 
Declare @Result as varchar(255)
    --If len(isnull(@strOrg,''))>0
If @type = 0
    --для денег
    Set @Result=Replace(Convert(varchar, Convert(money, @sum), 1), ',', ' ')
Else
    --для веса
    begin
        Set @Result=Convert(decimal(18,3),@sum,3)
        Set @Result=Replace(Convert(varchar, Convert(money, left(@Result,len(@Result)-1)), 1), ',', ' ')+right(@Result,1)
    end
 
    Return @Result
END
 
--------------------------------------------
 
-- построение общей строки на основе полей Organization, Name, Initials таблицы Clients
CREATE FUNCTION udf_ONI (@strOrg as varchar(255), @strName as varchar(55), @strInitials as varchar(2))  
RETURNS varchar(312)
AS  
BEGIN 
    Declare @strResult as varchar(312)
    
    If len(isnull(@strOrg,''))>0 Set @strOrg = '«' + @strOrg + '»'
    Else Set @strOrg = ''
 
    Set @strResult = rtrim(ltrim(@strOrg + ' ' + @strName + ' ' + isnull(@strInitials,'')))
 
    Return @strResult
END
 
------------------------------------
------------------------------------
Скрипты:
 
CREATE TABLE [dbo].[Clients] (
    [Id_Client] [int] NOT NULL ,
    [Id_Old] [int] NULL ,
    [Organization] [nvarchar] (255) COLLATE Cyrillic_General_CI_AS NULL ,
    [Name] [nvarchar] (55) COLLATE Cyrillic_General_CI_AS NOT NULL ,
    [Initials] [nvarchar] (2) COLLATE Cyrillic_General_CI_AS NULL ,
    [Zip] [nvarchar] (64) COLLATE Cyrillic_General_CI_AS NOT NULL ,
    [Zone] [smallint] NULL ,
    [Country] [nvarchar] (32) COLLATE Cyrillic_General_CI_AS NULL ,
    [Region] [nvarchar] (64) COLLATE Cyrillic_General_CI_AS NULL ,
    [Address] [nvarchar] (100) COLLATE Cyrillic_General_CI_AS NULL ,
    [Flat] [nvarchar] (32) COLLATE Cyrillic_General_CI_AS NULL ,
    [Rating] [int] NOT NULL ,
    [Rating_Old] [int] NULL ,
    [Memo_] [nvarchar] (20) COLLATE Cyrillic_General_CI_AS NULL ,
    [Iron] [bit] NOT NULL ,
    [Closed] [bit] NOT NULL ,
    [Error] [bit] NOT NULL ,
    [Sys] [bit] NOT NULL ,
    [User] [nvarchar] (16) COLLATE Cyrillic_General_CI_AS NULL ,
    [Date] [smalldatetime] NULL ,
    [Zone_Refresh] [bit] NOT NULL ,
    [Refresh] [bit] NOT NULL ,
    [Id_Customer] [int] NULL ,
    [Id_Ext] [int] NULL ,
    [memo] [nvarchar] (255) COLLATE Cyrillic_General_CI_AS NULL ,
    [LoginName] [nvarchar] (32) COLLATE Cyrillic_General_CI_AS NULL ,
    [PasswordName] [nvarchar] (32) COLLATE Cyrillic_General_CI_AS NULL 
) ON [PRIMARY]
GO

 CREATE  INDEX [IX_Clients] ON [dbo].[Clients]([Id_Client]) ON [PRIMARY]
GO
 
 CREATE  INDEX [IX_Name] ON [dbo].[Clients]([Name]) ON [PRIMARY]
GO
 
 CREATE  INDEX [IX_Customers] ON [dbo].[Customers]([Id_Customer]) ON [PRIMARY]
GO
 
 CREATE  INDEX [IX_Forms] ON [dbo].[Forms]([Id_Form]) ON [PRIMARY]
GO
 
 CREATE  INDEX [IX_Client] ON [dbo].[Forms]([Id_Client]) ON [PRIMARY]
GO
 
 CREATE  INDEX [IX_Orders] ON [dbo].[Orders]([Id_Order]) ON [PRIMARY]
GO
 
 CREATE  INDEX [IX_Form] ON [dbo].[Orders]([Id_Form]) ON [PRIMARY]
GO
 
 CREATE  INDEX [IX_Product] ON [dbo].[Orders]([Id_Product]) ON [PRIMARY]
GO
 
 CREATE  INDEX [IX_Products] ON [dbo].[Products]([Id_Product]) ON [PRIMARY]
GO
 
 CREATE  INDEX [IX_Customer] ON [dbo].[Products]([Id_Customer]) ON [PRIMARY]
GO