如何更新子类型的列值?
像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“已毕业”?