题解 | #某乎问答回答过教育类问题的用户里有多少用户回答过职场类问题#

select count(distinct author_id) as nun 
from answer_tb a left outer join issue_tb i
    on i.issue_id=a.issue_id
where i.issue_type='Career'
    and  a.author_id in (select author_id 
                            from answer_tb a left outer join issue_tb i
                            on i.issue_id=a.issue_id
                           where i.issue_type='Education')