declare
    column_exists exception;
    pragma exception_init (column_exists , -01430);
begin
    execute immediate 'ALTER TABLE TARIFA_VENDA_PACOTE ADD (USUARIO_CANCELAMENTO_ID NUMBER(7,0), MOTIVOCANCELVENDAPACOTE_ID NUMBER(7,0), INDCANCELADO NUMBER(1,0), DATACANCELAMENTO DATE)';
    exception when column_exists then null;
end;