intersect bug

Hi,

============================================================================
POSTGRESQL BUG REPORT TEMPLATE
============================================================================

Your name : Jan Vitek
Your email address : jvit8627(at)ss1000(dot)ms(dot)mff(dot)cuni(dot)cz

System Configuration
---------------------
Architecture (example: Intel Pentium) : AMD Pentium

Operating System (example: Linux 2.0.26 ELF) : Linux 2.2.10 ELF

PostgreSQL version (example: PostgreSQL-6.5.3): PostgreSQL-6.5.3

Compiler used (example: gcc 2.8.0) : gcc 2.7.2.3

Please enter a FULL description of your problem:
------------------------------------------------

Intersect operator doesn't work as it would under some circumstances,
which i describe below.

I have found this simplest example:

$ psql data <<EOF
create table num (n int4);
insert into num values (1);
insert into num values (null);
select * from num intersect select * from num;
select distinct * from num intersect select * from num;
drop table num;
EOF
create table num (n int4);
CREATE
insert into num values (1);
INSERT 448713 1
insert into num values (null);
INSERT 448714 1
select * from num intersect select * from num;
n
-
1

(2 rows)

select distinct * from num intersect select * from num;
n
-
1
(1 row)

drop table num;
DROP
$

I think that the result of the second select is wrong and should be the
same as the result of the first select. This behaviour happens only,
when there is a null in some field.

Jan Vitek <jvit8627(at)ss1000(dot)ms(dot)mff(dot)cuni(dot)cz>