with tmp as
(
    (select 
        uid,
        'exam' as type,
        date_format(start_time, '%Y%m') as act_month,
        date_format(start_time, '%Y%m%d') as act_day
    from exam_record
    where uid in
            (select
                uid
            from user_info
            where level in (6, 7)
            )
    )

union all

    (select 
        uid,
        'practice' as type,
        date_format(submit_time, '%Y%m') as act_month,
        date_format(submit_time, '%Y%m%d') as act_day
    from practice_record
    where uid in
        (select
            uid
        from user_info
        where level in (6, 7)
        )
    )
)

select 
    a.uid
    ,count(distinct act_month) as act_month_total
    ,count(distinct if(year(act_day) = 2021, act_day, null)) as act_days_2021
    ,count(distinct if(type = 'exam' and year(act_day) = 2021, act_day, null)) as act_days_2021_exam
    ,count(distinct if(type = 'practice' and year(act_day) = 2021, act_day, null)) as act_days_2021_question
from tmp
right join 
    (select
        uid
    from user_info
    where level in (6, 7)
    ) a -- 防止活躍數(shù)均為0的被忽略
on a.uid = tmp.uid
group by a.uid
order by act_month_total desc, act_days_2021 desc
;