--0: referencia de inventario
SELECT SRBSRO.SRSTHQ-SRBSRO.SRPICQ as Disponible,
    SRBSRO.SRSTHQ AS Existencia,
    SRBSRO.SRPICQ AS Reservado,
    SRBSRO.SRPURQ as EnOCs,
    SRBSRO.SRPRDC as Referencia,
    SRBSRO.SRSROM as Bodega
FROM SRBSRO
WHERE SRBSRO.SRPRDC='<$0$>'