declare
    column_exists exception;
    pragma exception_init (column_exists , -01430);
begin
    execute immediate 'ALTER TABLE AIDF ADD (PUNTOVENTA_ID NUMBER(7))';  
    exception when column_exists then null;
end;

/
declare
  object_exists  exception;
  except_02275  exception;
  except_02270  exception;

  pragma exception_init (object_exists  , -01430);
  pragma exception_init (except_02275  , -02275);
  pragma exception_init (except_02270  , -02270);
begin
    execute immediate 'ALTER TABLE AIDF ADD CONSTRAINT PUNTOVENTA_AIDF FOREIGN KEY (PUNTOVENTA_ID) REFERENCES PUNTO_VENTA (PUNTOVENTA_ID) ENABLE';  
  
  exception 
    when object_exists  then null;
    when except_02275  then null;
    when except_02270  then null;
end;
