mysql设置某个字段唯一

CREATE TABLE table_name (
    column1 datatype UNIQUE,
    column2 datatype,
    ...
);

ALTER TABLE table_name
ADD UNIQUE (column_name);

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50),
    email VARCHAR(100) UNIQUE,
    password VARCHAR(255)
);

ALTER TABLE users
ADD UNIQUE (email);

ERROR 1062 (23000): Duplicate entry 'example@example.com' for key 'email'

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