select  count(distinct us), count(distinct u), count(distinct q) 
from UserSession us , User u, UserSession q 
where q.question.id is not null

    /* select
        count(distinct us),
        count(distinct u),
        count(distinct q)
    from
        UserSession us ,
        User u,
        UserSession q
    where
        q.question is not null */ select
            count(distinct usersessio0_.USERSESSION_ID) as col_0_0_,
            count(distinct user1_.USER_ID) as col_1_0_,
            count(distinct usersessio2_.USERSESSION_ID) as col_2_0_
        from
            USERSESSION usersessio0_,
            USER user1_,
            USERSESSION usersessio2_
        where
            usersessio2_.QUESTION_ID is not null limit ?

@Entity
@Table(name = "USER")
@org.hibernate.annotations.Entity(selectBeforeUpdate = true)
public class User implements Serializable, Comparable   {

   @Id
   @GeneratedValue(strategy = GenerationType.AUTO)
   @Column(name = "USER_ID")
   private Long id;   
   
   @Column(name = "USERNAME", length = 20, nullable = false, unique = true)   
   private String username;
   
    @OneToOne(mappedBy = "user")
    private UserSession usersession;
   
   
       
   public User() {}

      ....etc
}



@Entity
@Table(name = "USERSESSION")
public class UserSession implements Serializable, Comparable   {
   
   @Id
   @GeneratedValue(strategy = GenerationType.AUTO)
   @Column(name = "USERSESSION_ID")
   private Long id;   
   
   @OneToOne
   @JoinColumn(name = "USER_ID")   
   private User user;
   
   @OneToOne
   @JoinColumn(name = "QUESTION_ID")   
   private Question question;
   
    
         public UserSession() {}

     .... etc

}