Suma de select

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Estimados:

Tengo esta consulta mysql quiero sumar datos dentro de otros select como lo muestro, la consulta me funciona menos con lo comentado como lo puedo hacer?

Código MySQL:

/*SELECT(SUM datos.AMOUNT*/
(SELECT 
    datos . *
FROM
    ((SELECT 
        EMP.rut as RUT,
            UPPER(CONCAT(EMP.name, ' ', EMP.surname)) as NOMBRE,
            DT.name as TIPO,
            TTR.docId as ID,
          
            IFNULL(SUM(-(TTR.netAmount)), 0) as AMOUNT,
            '' as MONTO_FONDO,
            '' as MONTO_RENDICION,
            '' as TOTAL,
            DATE_FORMAT(TEX.createdDate, '%d/%m/%Y') as FECHA_CREACION,
            ' ' as FECHA_PAGO,
            TEX.description as DESCRIPCION
    FROM
        TBL_EXPENSESREPORT TEX
    LEFT JOIN TBL_TRANSACTS TTR ON (TEX.id = TTR.docId AND TTR.deleted <> 1 AND TTR.docType = 7), TBL_DOCS_STATUS TDS, TBL_DOCS_TYPES DT, TBL_EMPLOYERS EMP
    WHERE
        TEX.deleted <> 1 AND DT.id = TTR.docType AND TEX.docStatus = TDS.id AND TEX.docStatus IN (3 , 5) AND TEX.created = EMP.uid AND TEX.createdDate BETWEEN '2014-09-01' AND '2014-09-30'
    GROUP BY EMP.rut) UNION ALL (SELECT 
        PF.employerId as RUT,
            UPPER(CONCAT(EMP.name, ' ', EMP.surname)) as NOMBRE,
            DT.name as TIPO,
            TTR.docId as ID,         
            IFNULL(SUM(TTR.netAmount), 0) as AMOUNT,-
            '' as MONTO_FONDO,
            '' as MONTO_RENDICION,
            '' as TOTAL,
            DATE_FORMAT(PF.date, '%d/%m/%Y') as FECHA_CREACION,
            DATE_FORMAT(PF.paymentDate, '%d/%m/%Y') as FECHA_PAGO,
            PF.name as DESCRIPCION
    FROM
        TBL_PAYFUNDS PF
    LEFT JOIN TBL_TRANSACTS TTR ON (PF.id = TTR.docId AND TTR.deleted <> 1 AND TTR.docType = 9), TBL_PAYFUNDSTATUS PFS, TBL_DOCS_TYPES DT, TBL_EMPLOYERS EMP
    WHERE
        PF.deleted <> 1 AND DT.id = TTR.docType AND PF.status = PFS.id AND PF.status = 4 AND PF.employerId = EMP.rut AND PF.date BETWEEN '2014-09-01' AND '2014-09-30'
    GROUP BY PF.employerId)) as datos
ORDER BY datos.rut , datos.FECHA_CREACION)) as total