Sql-server – should I include the primary key in the clustered index in order to make it unique

I have the following table:

IF OBJECT_ID('[dbo].[ShipTaxAddress]') IS NOT NULL 
DROP TABLE [dbo].[ShipTaxAddress] 
GO
CREATE TABLE [dbo].[ShipTaxAddress] ( 
[TaxRegionAddressId]  INT                              NOT NULL,
[TaxRegionId]         INT                              NOT NULL,
[CountryCode]         VARCHAR(2)                       NOT NULL,
[AddressFormatId]     INT                              NOT NULL,
[MatchAddressLine1]   NVARCHAR(50)                         NULL,
[MatchAddressLine2]   NVARCHAR(50)                         NULL,
[MatchAddressLine3]   NVARCHAR(50)                         NULL,
[MatchAddressLine4]   NVARCHAR(50)                         NULL,
[MatchAddressLine5]   NVARCHAR(50)                         NULL,
[MatchAddressLine6]   NVARCHAR(50)                         NULL,
[MatchPostalCode]     VARCHAR(20)                          NULL,
CONSTRAINT   [PK_ShipTaxAddress]  PRIMARY KEY CLUSTERED    ([TaxRegionAddressId] asc))

that has an identity as a clustered index.

however, as it is queried mostly according to these 2 columns:

[CountryCode]         VARCHAR(2)                       NOT NULL,
[AddressFormatId]     INT                              NOT NULL,

I thought about creating a clustered index on them.

they are pretty small, but they are not unique. should I include the id column in the cluster index so that I can make it unique?

Yes or No and Why?

This is the main query I would like to go faster:

ALTER PROCEDURE [dbo].[udpProductTaxRateGet]
(
    @itemNo varchar ( 20 ),
    @calculateDate datetime,
    @addressLine1 nvarchar( 50 ),
    @addressLine2 nvarchar( 50 ),
    @addressLine3 nvarchar( 50 ),
    @addressLine4 nvarchar( 50 ),
    @addressLine5 nvarchar( 50 ),
    @addressLine6 nvarchar( 50 ),
    @postalCode nvarchar( 20 ),
    @countryCode varchar( 2 ),
    @addressFormatID int
)
WITH EXECUTE AS 'webUserWithRW'
AS
--see Bocss2.dbo.[fnGetProductTax] for equivalent logic and comments in Bocss
DECLARE @Addresses TABLE (TaxRegionId int NOT NULL)

INSERT INTO @Addresses(TaxRegionId)
SELECT  DISTINCT TaxRegionId
FROM    dbo.[ShipTaxAddress]
WHERE   [CountryCode] = @countryCode
AND     [AddressFormatID] = @addressFormatID
AND     ISNULL (CONVERT(nvarchar(50),[MatchAddressLine1]), ISNULL(@addressLine1, '')) = ISNULL(@addressLine1, '')
AND     ISNULL (CONVERT(nvarchar(50),[MatchAddressLine2]), ISNULL(@addressLine2, '')) = ISNULL(@addressLine2, '')
AND     ISNULL (CONVERT(nvarchar(50),[MatchAddressLine3]), ISNULL(@addressLine3, '')) = ISNULL(@addressLine3, '')
AND     ISNULL (CONVERT(nvarchar(50),[MatchAddressLine4]), ISNULL(@addressLine4, '')) = ISNULL(@addressLine4, '')
AND     ISNULL (CONVERT(nvarchar(50),[MatchAddressLine5]), ISNULL(@addressLine5, '')) = ISNULL(@addressLine5, '')
AND     ISNULL (CONVERT(nvarchar(50),[MatchAddressLine6]), ISNULL(@addressLine6, '')) = ISNULL(@addressLine6, '')
AND     @postalcode Like ISNULL ( CONVERT(nvarchar(20),[MatchPostalCode]), @postalcode)




SELECT DISTINCT ISNULL(pst.TaxCode, '') as TaxCode
     , ISNULL(pst.TaxRate, 0) as TaxRate
FROM    dbo.[ProductShipTax] pst
        INNER JOIN
        @Addresses a
            ON pst.TaxRegionId = a.TaxRegionId
WHERE   pst.[ItemNo] = @itemNo
AND     @calculateDate BETWEEN pst.[DateFrom] AND pst.[DateTo]

GO

This is how I improved this procedure:

I have created the following indexes:

    CREATE INDEX IDX_ShipTaxAddress_ShipTaxAddress
    ON dbo.[ShipTaxAddress] (CountryCode,
                             AddressFormatID,
                             MatchPostalCode)
    INCLUDE (TaxRegionId,
             [MatchAddressLine1],
             [MatchAddressLine2],
             [MatchAddressLine3],
             [MatchAddressLine4],
             [MatchAddressLine5],
             [MatchAddressLine6])
    GO

     CREATE NONCLUSTERED INDEX IX_ProductShipTax_ITemNo_DateFrom_DateTo 
     ON [dbo].[ProductShipTax] (  [ItemNo] ASC  
                                , [DateFrom] ASC  
                                , [DateTo] ASC  )   
    INCLUDE (TaxRegionId ,TaxCode,TaxRate)
    WITH (DROP_EXISTING=ON)

I have changed the relevant columns in the table, from VARCHAR to NVARCHAR, in order to eliminate the need of conversion.
the Table became like this:

IF OBJECT_ID('[dbo].[ShipTaxAddress]') IS NOT NULL 
DROP TABLE [dbo].[ShipTaxAddress] 
GO
CREATE TABLE [dbo].[ShipTaxAddress] ( 
[TaxRegionAddressId]  INT                              NOT NULL,
[TaxRegionId]         INT                              NOT NULL,
[CountryCode]         VARCHAR(2)                       NOT NULL,
[AddressFormatId]     INT                              NOT NULL,
[MatchAddressLine1]   NVARCHAR(50)                         NULL,
[MatchAddressLine2]   NVARCHAR(50)                         NULL,
[MatchAddressLine3]   NVARCHAR(50)                         NULL,
[MatchAddressLine4]   NVARCHAR(50)                         NULL,
[MatchAddressLine5]   NVARCHAR(50)                         NULL,
[MatchAddressLine6]   NVARCHAR(50)                         NULL,
[MatchPostalCode]     NVARCHAR(20)                         NULL,
CONSTRAINT   [PK_ShipTaxAddress]  
PRIMARY KEY NONCLUSTERED ([TaxRegionAddressId] asc))
GO

I have changed the procedure:

ALTER PROCEDURE [DenormV2].[udpProductTaxRateGet]
(
    @itemNo varchar ( 20 ),
    @calculateDate datetime,
    @addressLine1 nvarchar( 50 ),
    @addressLine2 nvarchar( 50 ),
    @addressLine3 nvarchar( 50 ),
    @addressLine4 nvarchar( 50 ),
    @addressLine5 nvarchar( 50 ),
    @addressLine6 nvarchar( 50 ),
    @postalCode nvarchar( 20 ),
    @countryCode varchar( 2 ),
    @addressFormatID int
)
WITH EXECUTE AS 'webUserWithRW'
AS
--see Bocss2.dbo.[fnGetProductTax] for equivalent logic and comments in Bocss


SELECT @postalcode    = CASE WHEN @postalcode   = N'' THEN NULL ELSE @postalcode   END
SELECT @addressLine1  = CASE WHEN @addressLine1 = N'' THEN NULL ELSE @addressLine1 END
SELECT @addressLine2  = CASE WHEN @addressLine2 = N'' THEN NULL ELSE @addressLine2 END
SELECT @addressLine3  = CASE WHEN @addressLine3 = N'' THEN NULL ELSE @addressLine3 END
SELECT @addressLine4  = CASE WHEN @addressLine4 = N'' THEN NULL ELSE @addressLine4 END
SELECT @addressLine5  = CASE WHEN @addressLine5 = N'' THEN NULL ELSE @addressLine5 END
SELECT @addressLine6  = CASE WHEN @addressLine6 = N'' THEN NULL ELSE @addressLine6 END



SELECT TOP 1  ISNULL(pst.TaxCode, '') as TaxCode
            , ISNULL(pst.TaxRate, 0) as TaxRate
FROM    dbo.[ProductShipTax] pst
WHERE EXISTS (

    SELECT  TaxRegionId
    FROM    dbo.[ShipTaxAddress]
    WHERE   [CountryCode] = @countryCode
    AND     [AddressFormatID] = @addressFormatID

    AND ([MatchAddressLine1] = @AddressLine1 OR ([MatchAddressLine1] IS NULL AND @AddressLine1 IS NULL) )
    AND ([MatchAddressLine2] = @AddressLine2 OR ([MatchAddressLine2] IS NULL AND @AddressLine2 IS NULL) )
    AND ([MatchAddressLine3] = @AddressLine3 OR ([MatchAddressLine3] IS NULL AND @AddressLine3 IS NULL) )
    AND ([MatchAddressLine4] = @AddressLine4 OR ([MatchAddressLine4] IS NULL AND @AddressLine4 IS NULL) )
    AND ([MatchAddressLine5] = @AddressLine5 OR ([MatchAddressLine5] IS NULL AND @AddressLine5 IS NULL) )
    AND ([MatchAddressLine6] = @AddressLine6 OR ([MatchAddressLine6] IS NULL AND @AddressLine6 IS NULL) )

    AND (@postalcode = [MatchPostalCode]     OR ([MatchPostalCode]   IS NULL AND @postalcode   IS NULL) )
    AND  TaxRegionId = pst.TaxRegionId     

)
AND pst.[ItemNo] = @itemNo
AND @calculateDate BETWEEN pst.[DateFrom] AND pst.[DateTo]

GO

when comparing the following:

USE US16HSMMProduct_ORIGINAL
GO
exec dbo.udpProductTaxRateGet 
        @itemNo=N'31997299',
        @calculateDate='Aug  8 2016  1:01:46:760PM',
        @addressLine1=N'',
        @addressLine2=N'',
        @addressLine3=N'',
        @addressLine4=N'',
        @addressLine5=N'',
        @addressLine6=N'FL',
        @postalcode=N'',
        @countryCode=N'US',
        @addressFormatID=2
go
USE US16HSMMProduct_AFTER_CHANGES
GO
exec DenormV2.udpProductTaxRateGet
        @itemNo=N'31997299',
        @calculateDate='Aug  8 2016  1:01:46:760PM',
        @addressLine1=N'',
        @addressLine2=N'',
        @addressLine3=N'',
        @addressLine4=N'',
        @addressLine5=N'',
        @addressLine6=N'FL',
        @postalcode=N'',
        @countryCode=N'US',
        @addressFormatID=2
go

we get this:

here is the execution plan of the old procedure

here is the execution plan of the new procedure