mysql点击添加唯一约束

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,
    user_id INT NOT NULL,
    order_number VARCHAR(50) NOT NULL,
    UNIQUE (user_id, order_number)
);

-- 查找重复数据
SELECT username, COUNT(*)
FROM users
GROUP BY username
HAVING COUNT(*) > 1;

-- 删除重复数据（保留一条）
DELETE FROM users
WHERE id NOT IN (
    SELECT MIN(id)
    FROM users
    GROUP BY username
);

UPDATE users
SET username = CONCAT(username, '_', id)
WHERE id NOT IN (
    SELECT MIN(id)
    FROM users
    GROUP BY username
);