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#

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'