Как использовать if else в инструкции select в sql server 2008

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Мне нужно использовать оператор if else в операторе select ..Я создала СП, а после попытался

ALTER PROCEDURE [PR].[SPJ_PurchaseOrderDShipmentD]
--[PR].[SPJ_PurchaseOrderDShipmentD] 'FY12/PO/172'
    -- Add the parameters for the stored procedure here
@ParentDocCode varchar(50)
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;
SELECT distinct D.DocCode, D.FKFYCode, D.DocPrefix, D.DocNo, D.DocDate, D.FkItemCode,
D.FkItemName,D.FkItemName,
ISNULL((select InventoryUOMCode from MM.ITMIV where FkItemCode=D.FkItemCode),'0') as UOMCode,
ISNULL((select InventoryUOM from MM.ITMIV where FkItemCode=D.FkItemCode),'NA') as UOMName,

CAST(D.qty + (ISNULL((sELECT sUM(qty) FROM PR.PMDTL WHERE FkItemCode=D.FkItemCode AND ParentDocCode=D.DOCCODE),0)) AS Decimal(18,2)) as TotalPOQty,
CAST(ISNULL((sELECT sUM(QTY) FROM PR.PSDTL WHERE FkItemCode=D.FkItemCode AND ParentDocCode=D.DocCode ),0) AS Decimal(18,2)) PreviousIssuedQty,

CAST( Qty + (ISNULL((sELECT sUM(qty) FROM PR.PMDTL WHERE FkItemCode=D.FkItemCode AND ParentDocCode=D.DocCode),0)) - (
ISNULL((sELECT sUM(QTY) FROM PR.PSDTL WHERE FkItemCode=D.FkItemCode AND ParentDocCode=D.DocCode ) ,0)) AS Decimal(18,2))
 as Qty,0 as NextBalanceQty ,

case when P.Factor1=' '
then 0
else P.Factor1 as BrookerageAmt 

from pr.PODTL P where FkItemCode=D.FkItemCode and DocCode=@ParentDocCode)


--ISNULL((select Factor1 from PR.PODTL where FkItemCode=D.FkItemCode and DocCode=@ParentDocCode),0.00 ) as BrokerageAmt

 FROM
PR.POHDR H,PR.PODAC D
where D.DocCode=@ParentDocCode and d.DocCode = h.DocCode AND
Qty >0
 --(ISNULL((sELECT sUM(qty) FROM PR.PMDTL WHERE FkItemCode=D.FkItemCode AND ParentDocCode=D.DocCode),0)) -
 --(ISNULL((SELECT sUM(QTY) FROM PR.PSDTL WHERE FkItemCode=D.FkItemCode AND ParentDocCode=D.DocCode ),0) ) )> 0
and H.Status='Y' and D.Status='Y'


END

но получаю сообщение об ошибке, пожалуйста, помогите мне
любая помощь заметна
с уважением,
Шивани

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