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@xxxxxxxxxxxxxxxxx magproductions b.v. T: ++31(0)534346874 F: ++31(0)534346876 M: I: www.magproductions.nl A: Postbus 416 7500 AK Enschede // Integrate Your World //
