题解 | #回答过类问题的用户里有多少用户回答过B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
https://www.nowcoder.com/practice/b02cf9ee7b9f4cdda308f8155ff3415d
select
count(distinct if(issue_type = 'Career',author_id,null)) as num
from
answer_tb as a
left join issue_tb as b
on a.issue_id = b.issue_id
where a.author_id in(
select
author_id
from
answer_tb as t1
left join issue_tb as t2
using(issue_id)
where
issue_type = 'Education'
)
