SELECT
((SELECT sum(mueble1)  AS mueble1,
       sum(mueble2)  AS mueble2,
       sum(mueble3)  AS mueble3,
       sum(mueble4)  AS mueble4
FROM  stock_muebles)-

(SELECT sum(mueble1)  AS mueble1,
       sum(mueble2)  AS mueble2,
       sum(mueble3)  AS mueble3,
       sum(mueble4)  AS mueble4
FROM vv_muebles)) AS TOTAL