union query conditional

I am using following Union Query.
And its working like charm.

SELECT CM.CM_Date AS Cdate, CM.Cash_MemoNo AS CmNo,0 as BookDate, 0 as LR_No, CM.CM_Total as CMAmt, 0 as Amt_Rcvd, 0 as ChqDDNo, 0 as ChqDDdate, 0 as Acc_Typ, 0 as RcptNo,0 as MemoNo, 0 as M_Date, CM.CNee as conName
from (CashMemo as CM
INNER JOIN ClientLedger ON (ClientLedger.CName = CM.CNee))
UNION ALL SELECT Receipt_CLNT.Rcpt_Date, 0 as CmNo, 0 as BookDate, 0 as LR_No, 0 as CM_Total, Receipt_CLNT.Amt_Rcvd as RcptAmt,Receipt_CLNT.ChqDDNo as RefNo, Receipt_CLNT.ChqDDdate as RefDate, Receipt_CLNT.Amt_Mode as Mode, Receipt_CLNT.RcptNo as RcptNo, 0 as MemoNo, 0 as MDate, Receipt_CLNT.G_Name
from Receipt_CLNT
INNER JOIN ClientLedger ON (ClientLedger.CName = Receipt_CLNT.G_Name)
ORDER BY Cdate;

Select allOpen in new window

now a new field ( GrMod ) added in CashMemo table.
What i want is if GrMod = PAID then FROM CM_Total - CM.Freight else CM_Total
CM.Freight is not in this query but it is exist in CM table.
how can i do this..?
if GrMod = PAID then FROM CM_Total - CM.Freight else CM_Total