SELECT
    tag,
    t_cnt-cnt answer_cnt
FROM(
    SELECT
        tag,
        COUNT(*) cnt,
        SUM(COUNT(*)) OVER(PARTITION BY UPPER(tag)) t_cnt
    FROM
        examination_info ei
    INNER JOIN
        exam_record er
        ON ei.exam_id = er.exam_id
    GROUP BY
        tag
) t
WHERE
    tag != UPPER(tag) AND cnt < 3 AND t_cnt != cnt