python - 错误代码 1215 : Why Can't I Add Foreign Key

Question

我不明白为什么我无法将外键添加到我的表中...有人可以帮助我吗？这就是我遇到的问题:

CREATE TABLE Albums(
album_id INTEGER,
producer_id CHAR(6)NOT NULL,
release_date DATE,
album_title VARCHAR(30)NOT NULL,
price NUMERIC(5,2),
PRIMARY KEY(album_id),
FOREIGN KEY(producer_id)REFERENCES Musicians(sin));

上面的代码有效

CREATE TABLE Orders(
order_id INTEGER NOT NULL,
album_id INTEGER,
album_title VARCHAR(30)NOT NULL,
price NUMERIC(5,2),
PRIMARY KEY(order_id, album_id),
FOREIGN KEY (album_id) REFERENCES Albums(album_id),
FOREIGN KEY (album_title) REFERENCES Albums(album_title),
FOREIGN KEY (price) REFERENCES Albums(price));

但事实并非如此。我不知道为什么，但无法添加 album_title 和 Price 作为外键。

Answer 1

文档内容如下:

A FOREIGN KEY constraint does not have to be linked only to a PRIMARY KEY constraint in another table; it can also be defined to reference the columns of a UNIQUE constraint in another table.

因此，album_title 和 price 应该是 PRIMARY KEY，或者应该在 Albums 表中具有唯一约束。