From: | Alban Hertroys <alban(at)magproductions(dot)nl> |
---|---|
To: | Robert Haas <Robert(dot)Haas(at)dyntek(dot)com> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: complex referential integrity constraints |
Date: | 2007-02-19 09:12:42 |
Message-ID: | 45D96A0A.6030401@magproductions.nl |
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Lists: | pgsql-general |
Robert Haas wrote:
> So, I have the following problem.
>
> Suppose you have two kinds of animals, sheep and wolves. Since they
> have very similar properties, you create a single table to hold both
> kinds of animals, and an animal_type table to specify the type of each
> animal:
>
> CREATE TABLE animal_type (
> id integer not null,
> name varchar(80) not null,
> primary key (id)
> );
> INSERT INTO animal_type VALUES (1, 'Sheep');
> INSERT INTO animal_type VALUES (2, 'Wolf');
>
> CREATE TABLE animal (
> id serial,
> type_id integer not null references animal_type (id),
> name varchar(80) not null,
> age integer not null,
> weight_in_pounds integer not null,
> primary key (id)
> );
>
> The animal_type table is more or less written in stone, but the animal
> table will be updated frequently. Now, let's suppose that we want to
> keep track of all of the cases where one animal is mauled by another
> animal:
I kind of get the feeling that you'd want it like this:
CREATE TABLE predator (
...
) INHERITS animal;
And then put your foreign key constraints from predator to mauling.
You may want to be more accurate about what kind of animals sheep are as
well.
I haven't really given this much thought though, I'm just quickly
reading my mail before starting work ;)
--
Alban Hertroys
alban(at)magproductions(dot)nl
magproductions b.v.
T: ++31(0)534346874
F: ++31(0)534346876
M:
I: www.magproductions.nl
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