如何在数据库中插入多个下拉值？

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(255),
    email VARCHAR(255) UNIQUE,
    countries TEXT -- 存储国家的ID列表，以逗号分隔
);

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

INSERT INTO countries (name) VALUES ('USA'), ('Canada'), ('Mexico');

INSERT INTO users (name, email, countries) VALUES 
('John Doe', 'john@example.com', '1,2'), -- John选择了USA和Canada
('Jane Smith', 'jane@example.com', '2,3'); -- Jane选择了Canada和Mexico

SELECT u.name, u.email, GROUP_CONCAT(c.name) AS selected_countries
FROM users u
JOIN countries c ON FIND_IN_SET(c.id, u.countries)
GROUP BY u.id;

CREATE TABLE user_countries (
    user_id INT,
    country_id INT,
    PRIMARY KEY (user_id, country_id),
    FOREIGN KEY (user_id) REFERENCES users(id),
    FOREIGN KEY (country_id) REFERENCES countries(id)
);

INSERT INTO user_countries (user_id, country_id) VALUES 
(1, 1), -- John选择了USA
(1, 2), -- John选择了Canada
(2, 2), -- Jane选择了Canada
(2, 3); -- Jane选择了Mexico

SELECT u.name, u.email, GROUP_CONCAT(c.name) AS selected_countries
FROM users u
JOIN user_countries uc ON u.id = uc.user_id
JOIN countries c ON uc.country_id = c.id
GROUP BY u.id;