访问存储的对象

CREATE SEQUENCE test_seq START WITH 1001;

CREATE TABLE test_tab
(
   test_id  INTEGER,
   test_obj base_type,
   PRIMARY KEY (test_id)
);

INSERT INTO test_tab (test_id, test_obj)
VALUES (test_seq.nextval, base_type(1,'BASE_TYPE'));
INSERT INTO test_tab (test_id, test_obj)
VALUES (test_seq.nextval, base_type(2,'BASE_TYPE'));
INSERT INTO test_tab (test_id, test_obj)
VALUES (test_seq.nextval, mid_type(3, 'MID_TYPE',SYSDATE - 1));
INSERT INTO test_tab (test_id, test_obj)
VALUES (test_seq.nextval, mid_type(4, 'MID_TYPE',SYSDATE + 1));
INSERT INTO test_tab (test_id, test_obj)
VALUES (test_seq.nextval, leaf_type(5, 'LEAF_TYPE',SYSDATE - 20,'Maple'));
INSERT INTO test_tab (test_id, test_obj)
VALUES (test_seq.nextval, leaf_type(6, 'LEAF_TYPE',SYSDATE + 20,'Oak'));

返回对象引用：

SELECT test_id
      ,test_obj
  FROM test_tab;

返回对象引用，将 all 全部推送到子类型

SELECT test_id
      ,TREAT(test_obj AS mid_type) AS obj
  FROM test_tab;

按类型返回每个对象的字符串描述符

SELECT test_id
      ,TREAT(test_obj AS base_type).to_string() AS to_string -- Parenthesis are needed after the function name, or Oracle will look for an attribute of this name.
  FROM test_tab;