ORA-01408: such column list already indexed

create table tq84_ora_01408 (
    id   integer,
    grp  varchar2(20),
    val  number(7,2),
    --
    primary key (id, grp)
);

create index tq84_ora_01408_ix on tq84_ora_01408 (id, grp);

drop table tq84_ora_01408;