mysql建表语句 默认值

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'
);

-- 错误示例
CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) NOT NULL,
    email VARCHAR(100) NOT NULL,
    created_at TIMESTAMP DEFAULT 'now', -- 错误，默认值应为函数
    status VARCHAR(20) DEFAULT 'active'
);

-- 正确示例
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, -- 正确，默认值为函数
    status VARCHAR(20) DEFAULT 'active'
);

-- 错误示例
INSERT INTO users (username, email, created_at, status) VALUES ('user1', 'user1@example.com', NOW(), 'active');

-- 正确示例
INSERT INTO users (username, email) VALUES ('user1', 'user1@example.com'); -- 使用默认值
INSERT INTO users (username, email, created_at, status) VALUES ('user1', 'user1@example.com', DEFAULT, DEFAULT); -- 显式使用默认值