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#
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
http://www.nowcoder.com/practice/b02cf9ee7b9f4cdda308f8155ff3415d
select count(distinct t1.author_id) from answer_tb join issue_tb on answer_tb.issue_id=issue_tb.issue_id join (select distinct author_id from answer_tb join issue_tb on answer_tb.issue_id=issue_tb.issue_id where issue_type='Education' ) t1 on answer_tb.author_id=t1.author_id where issue_type='Career';