select t.OF_Feescode , t.OF_FeeHeadname,t.OF_FeeAmount, concession = (SELECT OF_FeesPercentage
FROM OF_Concession where OS_IdNo='4734' and OF_AcademicYear=(select acdyear from OP_Academicyear)
and OF_FeesHeadCode in ( SELECT OF_FeeHeadcode FROM OF_FeeHeads WHERE OF_GroupCode=1) and
OF_Feescode = t.OF_Feescode
), totalfee = sum(t.OF_FeeAmount + concession)
You cannot use an alias (concession in your example) that you have created in a select statement in another part of the select statement. So you will have to repeat the whole calculation, or do the calculation in a subquery or join. For example this should work:
SELECT t.OF_Feescode ,
t.OF_FeeHeadname ,
t.OF_FeeAmount ,
concession = OF_FeesPercentage,
totalfee = SUM(t.OF_FeeAmount + OF_FeesPercentage)
FROM tempTable t
CROSS APPLY
(
SELECT OF_FeesPercentage
FROM OF_Concession
WHERE OS_IdNo = '4734'
AND OF_AcademicYear = ( SELECT
acdyear
FROM OP_Academicyear
)
AND OF_FeesHeadCode IN ( SELECT
OF_FeeHeadcode
FROM OF_FeeHeads
WHERE
OF_GroupCode = 1 )
AND OF_Feescode = t.OF_Feescode
) c