mysql中间表怎么修改

INSERT INTO user_roles (user_id, role_id) VALUES (1, 3);

DELETE FROM user_roles WHERE user_id = 1 AND role_id = 2;

UPDATE user_roles SET created_at = NOW() WHERE user_id = 1 AND role_id = 3;

START TRANSACTION;
DELETE FROM user_roles WHERE user_id = 1 AND role_id = 2;
INSERT INTO user_roles (user_id, role_id) VALUES (1, 3);
COMMIT;

-- 创建用户表
CREATE TABLE users (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(255) NOT NULL
);

-- 创建角色表
CREATE TABLE roles (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(255) NOT NULL
);

-- 创建中间表
CREATE TABLE user_roles (
    user_id INT,
    role_id INT,
    PRIMARY KEY (user_id, role_id),
    FOREIGN KEY (user_id) REFERENCES users(id),
    FOREIGN KEY (role_id) REFERENCES roles(id)
);

-- 插入一些示例数据
INSERT INTO users (name) VALUES ('Alice');
INSERT INTO roles (name) VALUES ('Admin');
INSERT INTO roles (name) VALUES ('User');

-- 获取用户和角色的ID
SET @user_id = (SELECT id FROM users WHERE name = 'Alice');
SET @admin_role_id = (SELECT id FROM roles WHERE name = 'Admin');
SET @user_role_id = (SELECT id FROM roles WHERE name = 'User');

-- 修改中间表的关联关系
DELETE FROM user_roles WHERE user_id = @user_id AND role_id = @user_role_id;
INSERT INTO user_roles (user_id, role_id) VALUES (@user_id, @admin_role_id);