How to calculate Opening Balance / Balance Carried Forward in the SQL Query.

Hi,

This is the Query to calculate the Debit/Credit balance statement. However, I'm unable to calculate the Opening Balance/Balance Carried Forward this in query. Kindly help.

SELECT D.AC_NO,D.TRN_REF_NO,A.ACY_AVL_BAL,A.CCY,D.TRN_DT,
DECODE(D.DRCR_IND, 'D',D.LCY_AMOUNT,NULL) DEBIT,
DECODE(D.DRCR_IND, 'C',D.LCY_AMOUNT,NULL) CREDIT,
DECODE(D.AC_CCY,'AFS',D.LCY_AMOUNT,NULL) TXN_AMOUNT,
SUM (NVL(DECODE(D.DRCR_IND, 'C',D.LCY_AMOUNT,NULL),0)-NVL(DECODE(D.DRCR_IND, 'D',D.LCY_AMOUNT,NULL),0))
OVER (ORDER BY TRN_DT ROWS UNBOUNDED PRECEDING) BALANCE