select uid, count(if(submit_time is null,1,null)) a, 
count(submit_time) b,
group_concat(distinct concat_ws(':',date(start_time),tag) separator ';')
from exam_record left join examination_info using(exam_id)
where year(start_time)=2021
group by uid
having a>1 and a<5 and b>=1
order by a desc