declare
    object_exists exception;
    except_00904  exception;
	
    pragma exception_init (object_exists , -01430);
    pragma exception_init (except_00904 , -00904);
begin
    execute immediate 'ALTER TABLE PTOVTA_COMISSAO
	DROP (
		INDBILHETESTROCADOS, INDBILHETESTRANSFERIDOS
	)';
	
  exception 
	  when object_exists then null;
	  when except_00904 then null;
end;