mysql增加默认约束

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) NOT NULL,
    email VARCHAR(100) NOT NULL,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    status VARCHAR(20) DEFAULT 'active'
);

ALTER TABLE users
ADD COLUMN created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
ADD COLUMN status VARCHAR(20) DEFAULT 'active';

-- 错误的插入语句
INSERT INTO users (username, email) VALUES ('john_doe', 'john@example.com', '2023-10-01 12:00:00');

-- 正确的插入语句
INSERT INTO users (username, email) VALUES ('john_doe', 'john@example.com');

ALTER TABLE users
ALTER COLUMN created_at SET DEFAULT CURRENT_TIMESTAMP,
ALTER COLUMN status SET DEFAULT 'inactive';