mysql去重留一

DELETE
FROM
    sys_user
WHERE
    user_name IN (
        SELECT
            *
        FROM
            (
                SELECT
                    user_name
                FROM
                    sys_user
                GROUP BY
                    user_name
                HAVING
                    count(user_name) > 1
            ) t1
    )
AND user_id NOT IN (
    SELECT
        *
    FROM
        (
            SELECT
                min(user_id)
            FROM
                sys_user
            GROUP BY
                user_name
            HAVING
                count(user_name) > 1
        ) t2
)