mysql增加主码

CREATE TABLE users (
    id INT AUTO_INCREMENT,
    name VARCHAR(50),
    email VARCHAR(50),
    PRIMARY KEY (id)
);

ALTER TABLE users ADD PRIMARY KEY (id);

CREATE TABLE orders (
    order_id INT,
    customer_id INT,
    order_date DATE,
    PRIMARY KEY (order_id, customer_id)
);

ALTER TABLE orders ADD PRIMARY KEY (order_id, customer_id);

CREATE TABLE users (
    id INT AUTO_INCREMENT,
    name VARCHAR(50),
    email VARCHAR(50),
    PRIMARY KEY (id)
);

-- 检查重复值
SELECT id, COUNT(*)
FROM users
GROUP BY id
HAVING COUNT(*) > 1;

-- 删除重复值
DELETE FROM users
WHERE id IN (
    SELECT id
    FROM (
        SELECT id,
               ROW_NUMBER() OVER (PARTITION BY id ORDER BY id) AS row_num
        FROM users
    ) t
    WHERE row_num > 1
);