oracle - ORA-03113 の回避策: CAST MULTISET を使用した通信チャネルでのファイルの終わり

Question

以下の TEST_FUNCTION の呼び出しは、「ORA-03113: 通信チャネルのファイルの終わり」で失敗します。回避策は TEST_FUNCTION2 に示されています。私の実際の機能ははるかに複雑なので、コードを煮詰めました。Oracle 11G でテスト済み。最初の関数が失敗する理由を知っている人はいますか?

CREATE OR REPLACE TYPE "EMPLOYEE" AS OBJECT
(
    employee_id  NUMBER(38),
    hire_date    DATE
);

CREATE OR REPLACE TYPE "EMPLOYEE_TABLE" AS TABLE OF EMPLOYEE;

CREATE OR REPLACE FUNCTION TEST_FUNCTION RETURN EMPLOYEE_TABLE IS

table1        EMPLOYEE_TABLE;
table2        EMPLOYEE_TABLE;
return_table  EMPLOYEE_TABLE;
BEGIN

SELECT CAST(MULTISET
(
    SELECT user_id, created FROM all_users
    WHERE LOWER(username) < 'm'
) AS EMPLOYEE_TABLE)
INTO table1 FROM dual;

SELECT CAST(MULTISET
(
    SELECT user_id, created FROM all_users
    WHERE LOWER(username) >= 'm'
) AS EMPLOYEE_TABLE)
INTO table2 FROM dual;

SELECT CAST(MULTISET
(    
    SELECT employee_id, hire_date
      FROM TABLE(table1)
    UNION
    SELECT employee_id, hire_date
      FROM TABLE(table2)
) AS EMPLOYEE_TABLE)
INTO return_table FROM dual;

RETURN return_table;

END TEST_FUNCTION;



CREATE OR REPLACE FUNCTION TEST_FUNCTION2 RETURN EMPLOYEE_TABLE IS

table1        EMPLOYEE_TABLE;
table2        EMPLOYEE_TABLE;
return_table  EMPLOYEE_TABLE;
BEGIN

SELECT CAST(MULTISET
(
    SELECT user_id, created FROM all_users
    WHERE LOWER(username) < 'm'
) AS EMPLOYEE_TABLE)
INTO table1 FROM dual;

SELECT CAST(MULTISET
(
    SELECT user_id, created FROM all_users
    WHERE LOWER(username) >= 'm'
) AS EMPLOYEE_TABLE)
INTO table2 FROM dual;

WITH combined AS
(
    SELECT employee_id, hire_date
      FROM TABLE(table1)
    UNION
    SELECT employee_id, hire_date
      FROM TABLE(table2)
)
SELECT CAST(MULTISET
(
    SELECT * FROM combined
) AS EMPLOYEE_TABLE)
INTO return_table FROM dual;

RETURN return_table;

END TEST_FUNCTION2;





SELECT * FROM TABLE (TEST_FUNCTION()); -- Throws exception ORA-03113.

SELECT * FROM TABLE (TEST_FUNCTION2()); -- Works