postgresql - "polymorphism"用于 FOREIGN KEY 约束

Question

表中有这个字段:

room_id INT NOT NULL CONSTRAINT room_id_ref_room REFERENCES room

我有两种房间的三个 2 表:standard_room 和 family_room

如何做这样的事情:

room_id INT NOT NULL CONSTRAINT room_id_ref_room REFERENCES standard_room or family_room

我的意思是，room_id 应该引用或者 standard_room 或者 family_room。< br/> 有可能吗？

Answer 1

这是我一直在使用的模式。

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"
);

也就是说，“子类”通过类型描述符列指向父类(super class)(这样指向的基类是正确的类型，并且父类(super class)的主键与子类。