题解 | #每个用户的第一有效信息#

select device_id , case when answer_cnt then concat('答题数:',answer_cnt)
                        when gpa        then concat('gpa:',gpa)
                        when age        then concat('年龄:',age)
                        else '暂无关键信息' end as key_info  
from user_profile 
order by device_id;