Question

表格中有这个字段：

room_id INT NOT NULL CONSTRAINT room_id_ref_room REFERENCES room

我有两个房间的三个2桌：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 standard_room 或 family_room。
是否可以这样做？

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"
);

即，＆＃39;子类＆＃39;通过类型descriminator列指向超类（使得指向的基类具有正确的类型，并且超类的主键与子类相同。

FOREIGN KEY约束的“多态”

1 个答案: