That's not opening and closing balance - it's simply the amounts of the first and last transactions in the date range.

SELECT

a.AccNo,

t.Total_Adjustment,

t.Total_Topup,

t.Total_Comm,

t.Total_Transfer,

t.Total_RecvTransfer,

t.Total_Maxis,

t.Total_Digi,

t.Total_Celcom,

Option3.Open_Balance + t.TransactionsForPeriod AS ClosingBalance

FROM Tbl_Account a

LEFT JOIN (

SELECT

d.Transaction_AccNo,

SUM(d.Amount) AS TransactionsForPeriod,

SUM( case when d.TransType_ID = 0 then d.Amount else 0 end ) as Total_Adjustment,

SUM( case when d.TransType_ID = 1 then d.Amount else 0 end ) as Total_Topup,

SUM( case when d.TransType_ID = 2 then d.Amount else 0 end ) as Total_Comm,

SUM( case when d.TransType_ID = 3 then d.Amount else 0 end ) as Total_Transfer,

SUM( case when d.TransType_ID = 4 then d.Amount else 0 end ) as Total_RecvTransfer,

SUM( case when d.TransType_ID = 2 AND d.Topup_Company = 'M' then d.Amount else 0 end ) as Total_Maxis,

SUM( case when d.TransType_ID = 2 AND d.Topup_Company = 'D' then d.Amount else 0 end ) as Total_Digi,

SUM( case when d.TransType_ID = 2 AND d.Topup_Company = 'C' then d.Amount else 0 end ) as Total_Celcom

FROM (

SELECT

ti.Transaction_AccNo,

ti.TransType_ID,

p.Topup_Company,

Amount = SUM(ti.Amount)

FROM Tbl_Transaction ti

LEFT JOIN Tbl_Topup p ON p.Topup_ID = t.Topup_ID

WHERE ti.Transaction_Date >= convert(Date,'2012-09-1', 105)

AND ti.Transaction_Date < convert(Date,'2012-10-01', 105)

GROUP BY ti.Transaction_AccNo, ti.TransType_ID, p.Topup_Company

) d

GROUP BY d.Transaction_AccNo

) t

ON t.Transaction_AccNo = a.AccNo

OUTER APPLY ( -- SUM of all the amounts prior to date range

SELECT

Open_Balance = SUM(ti.Amount)

FROM Tbl_Transaction ti

WHERE ti.Transaction_AccNo = a.AccNo -- outer ref

AND ti.Transaction_Date < convert(Date,'2012-09-1', 105)

) Option3

ORDER BY a.AccNo