declare
    object_exists exception;
    pragma exception_init (object_exists , -01430);
begin
	execute immediate 'ALTER TABLE CLIENTE_DESCUENTO ADD (INDVENDER1PORCORRIDA NUMBER(1) DEFAULT 0 NOT NULL )';
	exception when object_exists then null;
end; 
/
declare
begin
	execute immediate 'UPDATE CLIENTE_DESCUENTO SET INDVENDER1PORCORRIDA = 0';
	exception when others then null;
end;