题解 | #某乎问答单日回答问题数大于等于3个的所有用户#
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 author_id) from answer_tb x join issue_tb using(issue_id) where issue_type = 'Career' and author_id in ( select distinct author_id from answer_tb x join issue_tb using(issue_id) where issue_type = 'Education' )