题解 | #回答过教育类问题的用户里有多少用户回答过职场类#
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 t1.author_id) num
from (
select
author_id
from answer_tb
where substr(issue_id,1,1) = 'E'
) t1
inner join (
select
author_id
from answer_tb
where substr(issue_id,1,1) = 'C'
) t2
on t1.author_id = t2.author_id
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