不同于我们最先映射的每个具体类一张表的策略，此处的表仅仅包含了每个非继承的属性（由子类本身声明的每个属性）以及也是超类表的外键的主键的列。
在Hibernate中，用<joined-subclass>元素给每个子类映射创建一张表。
<hibernate-mapping package="cn.jbit.hibernate.entity4"> <class name="BillingDetails6" table="BILLING_DETAILS6"> <id name="id" column="BILLING_DETAILS_ID" type="integer"> <generator class="native"/> </id> <property name="owner"> <column name="OWNER" not-null="true"/> </property> <joined-subclass name="CreditCard6" table="CREDIT_CARD6"> <key column="CREDIT_CARD_ID" /> <property name="number" column="CC_NUMBER" length="20" not-null="true"/> <property name="expMonth" column="EXP_MONTH" length="20" not-null="true"/> <property name="expYear" column="EXP_YEAR" length="20" not-null="true"/> </joined-subclass> </class> </hibernate-mapping>JPA中也有这个映射策略，即JOINED策略：
@Entity
@Table(name = "BILLING_DETAILS7")
@Inheritance(strategy = InheritanceType.JOINED)
public abstract class BillingDetails7 {
@Id
@GeneratedValue
@Column(name = "BILLING_DETAILS_ID", nullable = false)
private Integer id;
@Column(name = "OWNER", nullable = false)
private String owner;
}显式地指定列名，Hibernate就知道如何把表联结到一起。@Entity
@Table(name = "CREDIT_CARD7")
//子表主键名称，对应于BillingDetails7表外键
@PrimaryKeyJoinColumn(name="CREDIT_CARD_ID")
public class CreditCard7 extends BillingDetails7 {
@Column(name = "CC_NUMBER", nullable = false)
private String number;
@Column(name = "EXP_MONTH", nullable = false)
private String expMonth;
@Column(name = "EXP_YEAR", nullable = false)
private String expYear;
}下面是JPA XML描述符中与之相当的映射：<entity class="cn.jbit.hibernate.entity4.BillingDetails4" access="FIELD"> <inheritance strategy="JOINED"/> <attributes> <id name="id"> <column name="BILLING_DETAILS_ID" nullable="false"/> <generated-value strategy="AUTO"/> </id> <basic name="owner"> <column name="OWNER" nullable="false"/> </basic> </attributes> </entity> <entity class="cn.jbit.hibernate.entity4.CreditCard4" access="FIELD"> <primary-key-join-column name="CREDIT_CARD_ID"/> <attributes> <basic name="number"> <column name="CC_NUMBER" nullable="false"/> </basic> <basic name="expMonth"> <column name="EXP_MONTH" nullable="false"/> </basic> <basic name="expYear"> <column name="EXP_YEAR" nullable="false"/> </basic> </attributes> </entity>