“polymorphism” for FOREIGN KEY constraints

问题

There is this field in a table:

room_id INT NOT NULL CONSTRAINT room_id_ref_room REFERENCES room

I have three 2 tables for two kinds of rooms: standard_room and family_room

How to do something like this:

room_id INT NOT NULL CONSTRAINT room_id_ref_room REFERENCES standard_room or family_room

I mean, room_id should reference either standard_room or family_room.
Is it possible to do so?

回答1:

Here is the pattern I've been using.

CREATE TABLE room (
    room_id serial primary key,
    room_type VARCHAR not null,

    CHECK CONSTRAINT room_type in ("standard_room","family_room"),
    UNIQUE (room_id, room_type)
);

CREATE_TABLE standard_room (
    room_id integer primary key,
    room_type VARCHAR not null default "standard_room",

    FOREIGN KEY (room_id, room_type) REFERENCES room (room_id, room_type),
    CHECK CONSTRAINT room_type  = "standard_room"
);
CREATE_TABLE family_room (
    room_id integer primary key,
    room_type VARCHAR not null default "family_room",

    FOREIGN KEY (room_id, room_type) REFERENCES room (room_id, room_type),
    CHECK CONSTRAINT room_type  = "family_room"
);

That is, the 'subclasses' point at the super-class, by way of a type descriminator column (such that the pointed to base class is of the correct type, and that primary key of the super class is the same as the child classes.

来源：https://stackoverflow.com/questions/28222533/polymorphism-for-foreign-key-constraints