mysql 建立唯一性约束

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

CREATE TABLE orders (
    order_id INT AUTO_INCREMENT PRIMARY KEY,
    customer_id INT NOT NULL,
    order_date DATE NOT NULL,
    UNIQUE (customer_id, order_date)
);

try:
    cursor.execute("INSERT INTO users (username, email) VALUES (%s, %s)", ('user1', 'user1@example.com'))
    connection.commit()
except mysql.connector.IntegrityError as err:
    print(f"Error: {err}")

ALTER TABLE users DROP INDEX username;
ALTER TABLE users DROP INDEX email;

SELECT username, COUNT(*)
FROM users
GROUP BY username
HAVING COUNT(*) > 1;