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(*) from (
select a1.author_id,a1.issue_id,i2.issue_type from answer_tb as a1 left join issue_tb as i2
on a1.issue_id= i2.issue_id where
a1.author_id in
(
select a2.author_id from answer_tb as a2 left join issue_tb as i1
on a2.issue_id = i1.issue_id
where i1.issue_type='Education'
)) t1
where t1.issue_type = 'Career'
