如何更新oracle数据库中的subtype属性值？

Question

如何更新子类型的列值？

这样的代码无法访问学生的成绩属性：

update persons set grade = 'graduated';

CREATE OR REPLACE TYPE person (
    name varchar2(20),
    age number,
    address varchar2(20)
) NOT FINAL;

CREATE OR REPLACE TYPE student UNDER person (
    grade varchar2(20)
) NOT FINAL;

CREATE TABLE persons OF person;

INSERT INTO persons VALUES (student('Jon', 'undergraduate'));

如何将学生成绩更改为 'graduated'？

Answer 1

应该可行

update persons s set VALUE(s) = student(treat(value(s) as student).name, 'graduated');

Answer 2

我找到了问题的答案。
这是更新子类型属性的代码：

DECLARE
    s student;

BEGIN
    select treat(value(p) as student) into s from persons p where name = 'Jon';
    s.grade = 'graduated';
    update persons p set value(p) = s where name = 'Jon';
END;