Consider the following two tables and their primary keys:

create table testuser.test1 (
    col1 number not null,
    col2 number not null,
    col3 number not null
);
alter table testuser.test1
    add constraint test1_pk primary key (col1);

create table testuser.test2 (
    col1 number not null,
    col2 number not null,
    col3 number not null
);
create unique index testuser.test2_pk on testuser.test2 (col1);
alter table testuser.test2
    add constraint test2_pk primary key (col1)
    using index testuser.test2_pk;

Note that my index has the same name than my primary key: test2_pk.
If I compare the constraints and the indices, I cannot see any difference between the "automatic" index test1_pk and the "manual" index test2_pk.

select * from dba_indexes where table_owner = 'TESTUSER' and lower(index_name) like '%test%';
select * from dba_constraints where owner = 'TESTUSER' and lower(constraint_name) like '%test%';

But obviously, Oracle can tell the difference, because if I now drop the primary keys and check my indices again:

alter table testuser.test1 drop constraint test1_pk;
alter table testuser.test2 drop constraint test2_pk;

select * from dba_indexes where table_owner = 'TESTUSER' and lower(index_name) like '%test%';

the "automatic" index test1_pk is gone, but the "manual" index test2_pk is still here (as it should)


My question is: How can I know if an index is "automatic" (i.e. will be dropped when dropping the primary key) or "manual" (won't be dropped when dropping the primary key) ?