Utiliser un index couvrant

Question

La table actor possède un index idx_actor_last_name sur la colonne last_name. Laquelle des requêtes suivantes peut utiliser cet index comme index couvrant ?

Answer 1

select last_name, last_update from actor order by last_name desc;

Answer 2

select distinct last_name from actor;

Answer 3

select last_name from actor order by last_update;

Answer 4

select last_name, count(*) from actor group by last_name;