ALTER TABLE Cbtes_Cond_Vtas ADD Plazo_Venc SmallInt
GO 

update cbtes_cond_vtas set plazo_venc = 0  where Plazo_Venc is null
go
update cbtes_cond_vtas set Porc_Desc_Liquidacion = 0  where Porc_Desc_Liquidacion is null
go
update cbtes_cond_vtas set Porc_Desc_Fact = 0  where Porc_Desc_Fact is null
go