mysql查询约束名

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) UNIQUE,
    email VARCHAR(100) UNIQUE,
    age INT CHECK (age >= 0 AND age <= 120),
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- 错误示例
INSERT INTO users (id, username, email) VALUES (1, 'user1', 'user1@example.com');

-- 正确示例
INSERT INTO users (id, username, email) VALUES (2, 'user2', 'user2@example.com');

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

-- 正确示例
INSERT INTO users (username, email) VALUES ('user3', 'user3@example.com');

-- 错误示例
CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    user_id INT,
    FOREIGN KEY (user_id) REFERENCES users(id)
);

INSERT INTO orders (order_id, user_id) VALUES (1, 999);

-- 正确示例
INSERT INTO orders (order_id, user_id) VALUES (1, 1);