One of my fields are null and I am trying to use distinct to filter out the redundant and records which are repeated. This is my SQL statement which calculates checks value based on being drawn and not!

SELECT   CASE SUM(Money)
             WHEN null THEN sum(0)
             ELSE SUM(Money)
         END AS MoneyTaken
FROM     (SELECT   Money
          FROM     tblPayment AS tblPayment_1
          WHERE    (CheckStatus = 0) AND (IDBuyer = @BuyerID) AND (IDSource = @SourceID)
          GROUP BY ID, IDBuyer, IDSeller, Money) AS derivedtbl_1_1) AS [Cheques Which didnt have credit], tblPurchase.Price AS SellPrice

but this doesn't work and I still get NULL in MoneyTaken Column when executing the function.

This is my full stored procedure which still shows repeated results :

ALTER PROCEDURE [dbo].[SGetListofKharIDBuyer]
@SurceId bigint,
@BuyerId bigint
AS
    SET NOCOUNT ON;
    /*
    0 = check(cheque)  dosent have credit-so couldntget money out of it
    1 = check(cheque) has credit- got the money
   -1 = in cashe  - paid in cash
    */

SELECT     distinct   vPatmentForReport.Account, vPatmentForReport.PaymentStatus, vPatmentForReport.Description, vPatmentForReport.Bank, vPatmentForReport.Serial, 
                         vPatmentForReport.PaymentMethod, vPatmentForReport.Date, vPatmentForReport.مبلغ * Money AS [Payment in Cash], tblPurchase.Date AS [PurchaseDate], 
                         tblReserve.Fee , tblReserve.NumberOfReserve , tblReserve.TotalMoney ,
                             (SELECT         COALESCE( SUM(Money),0) AS [PaidMoney]
                                FROM            (SELECT        Money
                                                           FROM            tblPardakht
                                                           WHERE        (CheckStatus <> 0) AND (IDBuyer = @BuyerId) AND (IDSource = @SurceId)
                                                           GROUP BY ID, IDBuyer, IDAccount, Money) AS derivedtbl_1) AS [Sum of Cheques and in cash payments],
                             (SELECT       COALESCE( SUM(Money),0) AS [PaidMoney]
                                FROM            (SELECT        Money
                                                           FROM            tblPardakht AS tblPardakht_1
                                                           WHERE        (CheckStatus = 0) AND (IDBuyer = @BuyerId) AND (IDSource = @SurceId)
                                                           GROUP BY ID, IDBuyer, IDAccount, Money) AS derivedtbl_1_1) AS [sum of cheques which are not drawn], tblPurchase.Money , 
                         tblReserve.Description , tblReserve.Date
FROM            tblPurchase INNER JOIN
                         tblReserve ON tblPurchase.IDReserve = tblReserve.ID inner JOIN
                         vPatmentForReport ON tblReserve.IDSource = vPatmentForReport.[SourceId] AND tblReserve.IDBuyer = vPatmentForReport.[BuyerId]
WHERE        (vPatmentForReport.[BuyerId] = @BuyerId) AND (vPatmentForReport.[SourceId] = @SurceId)

vPatmentForReport is a view which is made by a function without any parameters.