Android Sqlite update and insert only the biggest _id

I m' trying to update values only where there is the max id like this :

Cursor c = db.rawQuery("SELECT MAX(_id) FROM test3 ", null);
            if (c.moveToFirst()) {
                db.execSQL("UPDATE test3 SET mac='" + MAC + "',mdp='" + MDP + "'");

But all my rows change and became the same that i choose just before and i just want the maximum to change

My database is define like this :

 db = openOrCreateDatabase("testDB3", Context.MODE_PRIVATE, null);
    db.execSQL("CREATE TABLE IF NOT EXISTS test3(_id INTEGER PRIMARY KEY,mac VARCHAR,mdp VARCHAR,obj VARCHAR);");