mysql 往表里写数据库

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) NOT NULL,
    email VARCHAR(100) NOT NULL UNIQUE
);

INSERT INTO users (username, email) VALUES ('john_doe', 'john@example.com');

-- 错误示例，主键冲突
INSERT INTO users (id, username, email) VALUES (1, 'jane_doe', 'jane@example.com');

-- 正确示例，让MySQL自动生成主键值
INSERT INTO users (username, email) VALUES ('jane_doe', 'jane@example.com');

-- 错误示例，违反唯一约束
INSERT INTO users (username, email) VALUES ('john_doe', 'john@example.com');

-- 正确示例，先检查再插入
SELECT * FROM users WHERE email = 'john@example.com';
-- 如果没有结果，则插入
INSERT INTO users (username, email) VALUES ('john_doe', 'john@example.com');

-- 错误示例，语法错误
INSERT INTO users (username, email VALUES ('john_doe', 'john@example.com');

-- 正确示例
INSERT INTO users (username, email) VALUES ('john_doe', 'john@example.com');