Re: Updating cidr column with network operator

Michael Fuhr wrote:
> On Mon, Sep 26, 2005 at 12:34:59PM +0200, Axel Rau wrote:
>
>>Am 26.09.2005 um 02:05 schrieb Michael Fuhr:
>>
>>>On Fri, Sep 23, 2005 at 09:19:25PM +0200, Axel Rau wrote:
>>>
>>>>I'm sure this would be the cleanest solution but remember networks
>>>>change.
>>>
>>>Yes, which is why it's a good idea to automatically propogate those
>>>changes to tables that maintain redundant data.
>>
>>I would not call it redundant but normalized, because network has some
>>attributes, common to all addresses in the net, 1st of all the netmask.
>
>
> An attribute is redundant if it repeats a fact that can be learned
> without it. If one table contains IP addresses and another contains
> networks, then you can associate IP addresses and networks with a
> join of the two tables; indeed, this is how the "fix the network
> column" update works. Having a network column in the address table
> simply repeats what could be learned through the join.
>
>

I agree with Michael here. I think the fundamental problem with your
schema is that it is possible to have contradictory data between the
network and address table, always a bad situation.

I would replace network.id with a serial type value and make the cidr a
separate column, for example:

CREATE TABLE network (
id int not null PRIMARY KEY,
address cidr not null,
attr1 varchar(10) null
);

CREATE TABLE address (
id inet PRIMARY KEY,
network int NOT NULL
REFERENCES network
);

insert into network( id, address, attr1 ) values( 1, '10.1', 'a' );
insert into network( id, address, attr1 ) values( 2, '10.2', 'b' );
go

insert into address( id, network ) values( '10.1.0.1', 1 );
insert into address( id, network ) values( '10.1.0.2', 1 );
insert into address( id, network ) values( '10.1.0.3', 1 );
-- OOPS!
insert into address( id, network ) values( '10.2.0.4', 1 );
go

-- This will "correct" the any addresses put in the wrong network
update address
set network = ( select id from network where address >> address.id )

[additional network stuff snipped]

--
Daryl

"We want great men who, when fortune frowns, will not be discouraged."
-- Colonel Henry Knox, 1776