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