为什么spring jpa在相关表格中创建标记为“唯一”的列？

Question

我有一个使用Spring JPA，hibernate，Derby数据库的Spring Boot应用程序，具有以下实体和关系;

@Entity
@Table(name = "users")
public class User implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", nullable = false, updatable = false)
    private Long id;

    @Column(name = "email", nullable = false, unique = true)
    private String email;

    //bi-directional one-to-one association to Profile
    @OneToOne(cascade={CascadeType.ALL}, orphanRemoval=true)
    @JoinColumn(name="profile_id")
    private Profile profile;

    // ... other fields + getters & setters 
}

然后我有一个相关的实体，如下所示;

@Entity
@Table(name = "profiles")
public class Profile implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", nullable = false, updatable = false)
    private Long id;

    //bi-directional one-to-one association to User
    @OneToOne(mappedBy="profile")
    private User user;

    @Column(name = "first_name", nullable = false)
    private String firstname;

    @Column(name = "last_name", nullable = false)
    private String lastname;

    // ... other fields + getters & setters 
}

奇怪的是，我注意到当我运行应用程序并从实体创建数据库表时，也会在配置文件表中创建电子邮件列，即使实体未声明电子邮件字段。

1。有人可以首先解释为什么会这样吗？

2. 如何确保个人资料表没有电子邮件列？