题解 | 应该是对的吧

SELECT
    uid,
    nick_name,
    achievement
FROM user_info
WHERE nick_name LIKE '牛客%号'
    AND achievement BETWEEN 1200 AND 2500
    AND uid IN (
        SELECT uid
        FROM (
            SELECT uid, start_time AS act_time
            FROM exam_record
            UNION ALL
            SELECT uid, submit_time AS act_time
            FROM practice_record
        ) temp
        GROUP BY uid
        HAVING DATE_FORMAT(MAX(act_time), '%Y%m') = 202109
    )