题解 | 根据指定记录是否存在输出不同情况

SELECT 
  ui.uid,
  count(start_time)-count(submit_time) AS incomplete_cnt,
  ROUND((count(start_time)-count(submit_time))/COUNT(1),3) as incomplete_rate
FROM exam_record er 
right JOIN user_info ui

on ui.uid = er.uid
WHERE 
if((select max(incomplete_cnt) from (select count(1)-count(submit_time) incomplete_cnt from exam_record where uid in (select distinct uid from user_info where level=0))t)>2 ,`level`=0,start_time is not null)
GROUP BY uid
ORDER BY incomplete_rate ASC