mysql 多态关联

CREATE TABLE posts (
    id INT PRIMARY KEY AUTO_INCREMENT,
    title VARCHAR(255),
    content TEXT,
    author_id INT,
    author_type VARCHAR(50)
);

CREATE TABLE authors (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(255)
);

CREATE TABLE commenters (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(255)
);

INSERT INTO authors (name) VALUES ('John Doe');
INSERT INTO commenters (name) VALUES ('Jane Smith');

INSERT INTO posts (title, content, author_id, author_type) VALUES 
('My First Post', 'This is the content of my first post', 1, 'authors'),
('My Second Post', 'This is the content of my second post', 1, 'commenters');

SELECT p.title, a.name AS author_name
FROM posts p
JOIN authors a ON p.author_id = a.id AND p.author_type = 'authors'
WHERE p.id = 1;

SELECT p.title, c.name AS commenter_name
FROM posts p
JOIN commenters c ON p.author_id = c.id AND p.author_type = 'commenters'
WHERE p.id = 2;