How to CREATE VIEW to merge two tables each of which has CLOB-typed column

Question

I failed in creating a view to merge two tables that have CLOB-type column each.
The details are:
Database: Oracle 9i (9.2.0)
Two tables "test" and "test_bak", each of which has the following structure:
ID Number(10, 0)
DUMMY VARCHAR2(20)
DUMMYCLOB CLOB
The following operation fails:
create view dummyview (id, dummy, dummyclob) as
select id, dummy, dummyclob from test
union
select id, dummy, dummyclob from test_bak;
I was announced:
select test.id, test.dummy, test.dummyclob
ERROR in line 2:
ORA-00932: inconsistent data type: required - , but CLOB presented.
But if creating views from only ONE table with CLOB-type columns, or from two tables WITHOUT CLOB-typed columns, the creation will succeed. The following 1) and 2) will succeed, both:
1) one table, with CLOB-typed column
create view dummyview (id, dummy, dummyclob) as
select id, dummy, dummyclob from test;
2) two tables, without CLOB-typed columns
create view dummyview (id, dummy) as
select id, dummy from test
union
select id, dummy from test_bak;
I want to merge the two tables all, with complete columns, how to write the CREATE VIEW SQL statement?
many thanks in advance

Answer 1

Dong Wenyu,
No.
But you could do this:
SELECT source.*, nvl (tab1.clob_column, tab2.clob_column)
FROM your_table1 tab1, your_table2 tab2, (
SELECT primary_key, ...
FROM your_table1
UNION
SELECT primary_key, ...
FROM your_table2
) source
WHERE source.primary_key = tab1.id (+)
AND source.primary_key = tab2.id (+)
In other words, do the set operation (UNION (ALL)/INTERSECT/MINUS) on just the PK columns before pulling in the LOB columns.
d.