@Entity
@Table(name="tbl_user")
public class User implements Serializable
{
   @Id
  @GeneratedValue(strategy=GenerationType.AUTO)
   private Integer id;
 
  @Column(nullable=false, length=100)
   private String username;
 
  @Column(nullable=false, length=100)
   private String password;
 
  @OneToOne(mappedBy="user", fetch=FetchType.LAZY, cascade=CascadeType.ALL)
   private Customer customer;
............................
}

@Entity
@Table(name="tbl_customer")
public class Customer implements Serializable
{
   @Id
  @GeneratedValue(strategy=GenerationType.AUTO)
   private Integer id;
 
  @Column(nullable=false, length=50)
   private String firstName;
 
  @Column(length=1)
   private String middleInitial;
 
  @Column(nullable=false, length=50)
   private String lastName;
 
  @Column(nullable=false, length=100)
   private String email;
 
  @Column(nullable=false, length=15)
   private String phone;
 
  @OneToOne(fetch=FetchType.LAZY)
   private User user;
.............................
}

public List<User> getAllUsers()
{
  return this.em.createQuery("select u from User u").getResultList();
}

Hibernate:
    /* select
        u
    from
        User u */ select
            user0_.id as id106_,
            user0_.active as active106_,
            user0_.password as password106_,
            user0_.userGroup_id as userGroup5_106_,
            user0_.username as username106_
        from
            tbl_user user0_
Hibernate:
    /* load com.agribeef.abcommerce.model.Customer */ select
        customer0_.id as id97_0_,
        customer0_.email as email97_0_,
        customer0_.firstName as firstName97_0_,
        customer0_.lastName as lastName97_0_,
        customer0_.middleInitial as middleIn5_97_0_,
        customer0_.phone as phone97_0_,
        customer0_.user_id as user7_97_0_
    from
        tbl_customer customer0_
    where
        customer0_.user_id=?
Hibernate:
    /* load com.agribeef.abcommerce.model.Customer */ select
        customer0_.id as id97_0_,
        customer0_.email as email97_0_,
        customer0_.firstName as firstName97_0_,
        customer0_.lastName as lastName97_0_,
        customer0_.middleInitial as middleIn5_97_0_,
        customer0_.phone as phone97_0_,
        customer0_.user_id as user7_97_0_
    from
        tbl_customer customer0_
    where
        customer0_.user_id=?
.........................................................