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)
from answer_tb
where issue_id in (select issue_id 
                   from issue_tb 
                   where issue_type='Career')
      and author_id in (select author_id
                        from answer_tb
                        where issue_id in (select issue_id 
                                           from issue_tb 
                                           where issue_type='Education'))