我正在试着做一个r.d.b.，但外键好像没法用。运行程序时，会创建两个没有外键（words和pdf）的表，然后索引表中会出现运行时错误：
表“index”包含列“wordid”不在表中的约束定义。德比正常关机
这是我的密码：

new String createSQL3 = "create table Index (" 
        + " IndexID integer not null generated always as"
        + " identity (start with 1, increment by 1),"
        + " IndexPage integer not null, IndexOccurences integer not null,"
        + " constraint IndexID_PK primary key (IndexID),"
        + " constraint WordID_FK FOREIGN KEY (WordID) REFERENCES Words(WordID),"
        + " constraint PDFID_FK FOREIGN KEY (PDFID) REFERENCES PDFs(PDFID))";

        statement.execute(createSQL3);
        System.out.println("Table Index created successfully");

        connection.commit();

    } catch (SQLException EX) {
        System.out.println(EX.getMessage());