FULL JOIN: macaddr equality is not a mergejoinable join condition?

Try this:

create table interface ( mac macaddr, primary key(mac) );

insert into interface (mac) values ('00:11:22:33:44:55');
insert into interface (mac) values ('00:11:22:33:44:5a');
insert into interface (mac) values ('00:11:22:33:44:5f');

create table host (
mac macaddr,
ip inet,
foreign key (mac) references interface,
primary key (ip)
);

insert into host ( mac, ip ) values ('00:11:22:33:44:55', '192.168.1.1');
insert into host ( mac, ip ) values (null, '192.168.1.2');

select * from interface full join host using (mac);
ERROR:  FULL JOIN is only supported with mergejoinable join conditions


If you replace the "macaddr" columns with "varchar(17)":

        mac        |     ip
-------------------+-------------
 00:11:22:33:44:55 | 192.168.1.1
 00:11:22:33:44:5a |
 00:11:22:33:44:5f |
                   | 192.168.1.2


Why? This seems like a bug. Running on postgresql 7.1.3, compiled from the
source RPM on the download site. If people could CC any replies to my email,
I'd be grateful.


--
Regards,
Phil

+------------------------------------------+
| Phil Mayers                              |
| Network & Infrastructure Group           |
| Information & Communication Technologies |
| Imperial College                         |
+------------------------------------------+