type problems during union: NULL+NULL produces TEXT

Hi,

I have three tables, two of which are missing a column:

CREATE TABLE table1 (t1 TEXT);
CREATE TABLE table2 (t2 TEXT);
CREATE TABLE table3 (t3 TEXT, i3 INTEGER);

I am trying to create a view over these tables that defaults values for
non-existant columns to NULL.

CREATE VIEW view1 (i, t) AS
SELECT t1, NULL FROM table1
UNION ALL
SELECT t2, NULL FROM table2
UNION ALL
SELECT t3, i3 FROM table3
;

This fails with

ERROR: UNION types 'text' and 'integer' not matched

suggesting that NULL+NULL produces TEXT as type of the second column in
the union. The plain select (without CREATE VIEW) fails in the same way.

It works for two tables (NULL+INTEGER = INTEGER):

CREATE VIEW view2 (i, t) AS
SELECT t1, NULL FROM table1
UNION ALL
SELECT t3, i3 FROM table3
;

and of course with explicit casts

CREATE VIEW view3 (i, t) AS
SELECT t1, NULL::integer FROM table1
UNION ALL
SELECT t2, NULL::integer FROM table2
UNION ALL
SELECT t3, i3 FROM table3
;

Best wishes, Mike

PS: This is version()
'PostgreSQL 7.3.1 on i686-pc-linux-gnu, compiled by GCC 2.95.4'.

--
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