Expression #1 of ORDER BY clause is not in GROUP BY clause and contains nonaggregated column 'kmqfhzdb_puli.o.id_oferta' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

SELECT p.id_producto FROM productos p, ofertas o WHERE o.id_producto=p.id_producto GROUP BY p.id_producto ORDER BY o.id_oferta