MySQL - convertir a char un dato double

SELECT FORMAT(SUM(ImpGT),2) AS ImpGT,

       FORMAT(SUM(ImpXB),2) AS ImpXB,

	   FORMAT(SUM(OtrosImp),2) AS OtrosImp,

	   FORMAT(SUM(PagosAnticip),2) AS PagosAnticip,

	   FORMAT(SUM(CreditoFavor),2) AS CreditoFavor,

	   CONVERT(SUM(FORMAT(SubTotal,2) ) ,CHAR)  AS Total

FROM (

  SELECT 0 AS ImpGT, 0 AS ImpXB, 0 AS OtrosImp, SUM(PagoCC) AS PagosAnticip, SUM(Comision) AS CreditoFavor, 0 AS SubTotal FROM Servicios WHERE Tipo<>'BSP' AND TipoDocAsoc='PAG' AND DocAsoc=27284

  UNION

  SELECT SUM(`TAXxTKT`.`Amount`) AS ImpGT, 0 AS ImXB, 0 AS OtrosImp, SUM(`Servicios`.`PagoCC`) AS PagosAnticip, SUM(`Servicios`.`Comision`) AS CreditoFavor, SUM(Servicios.PrecioVenta*Servicios.RoeAgencia) AS SubTotal FROM `TAXxTKT`, `Tickets`, `Servicios`  WHERE `TAXxTKT`.`TAX`='GT' AND `TAXxTKT`.`TKTType`=`Tickets`.`TKTType` AND  `TAXxTKT`.`TKT`=`Tickets`.`Ticket` AND `Tickets`.`Servicio`=`Servicios`.`Servicio` AND `Servicios`.`TipoDocAsoc`='PAG' AND `Servicios`.`DocAsoc`=27284

  UNION

  SELECT 0 AS ImpGT, SUM(`TAXxTKT`.`Amount`) AS ImXB, 0 AS OtrosImp, 0 AS PagosAnticip, 0 AS CreditoFavor, 0 AS SubTotal FROM `TAXxTKT`, `Tickets`, `Servicios`  WHERE `TAXxTKT`.`TAX`='XB' AND `TAXxTKT`.`TKTType`=`Tickets`.`TKTType` AND  `TAXxTKT`.`TKT`=`Tickets`.`Ticket` AND `Tickets`.`Servicio`=`Servicios`.`Servicio` AND `Servicios`.`TipoDocAsoc`='PAG' AND `Servicios`.`DocAsoc`=27284

  UNION

  SELECT 0 AS ImpGT, 0 AS ImXB, SUM(`TAXxTKT`.`Amount`) AS OtrosImp, 0 AS PagosAnticip, 0 AS CreditoFavor, 0 AS SubTotal FROM `TAXxTKT`, `Tickets`, `Servicios`  WHERE `TAXxTKT`.`TAX`<>'GT' AND `TAXxTKT`.`TAX`<>'XB' AND `TAXxTKT`.`TKTType`=`Tickets`.`TKTType` AND  `TAXxTKT`.`TKT`=`Tickets`.`Ticket` AND `Tickets`.`Servicio`=`Servicios`.`Servicio` AND `Servicios`.`TipoDocAsoc`='PAG' AND `Servicios`.`DocAsoc`=27284

 union

 SELECT 0 AS ImpGT, 0 AS ImXB, 0 AS OtrosImp, 0 AS PagosAnticip, 0 AS CreditoFavor,(SELECT SUM(PrecioVenta*RoeAgencia) FROM Servicios  WHERE TipoDocAsoc='PAG' AND DocAsoc=27284 ) AS Subtotal

) AS PiePagina;