if not exists(select 1 from syscolumns where id = object_id('EST_ARV_MERC_LINHA') and name = 'PERC_DESCONTO')
begin 
ALTER TABLE dbo.EST_ARV_MERC_LINHA ADD
	PERC_DESCONTO money NOT NULL CONSTRAINT DF_EST_ARV_MERC_LINHA_PERC_DESCONTO DEFAULT 0
end