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
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
https://www.nowcoder.com/practice/b02cf9ee7b9f4cdda308f8155ff3415d
select count(*) as num from answer_tb a join issue_tb using (issue_id) where issue_type = 'Career' and a.author_id in ( select author_id from answer_tb join issue_tb using (issue_id) where issue_type = 'Education')
