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

with a as(
    select
        author_id
    from 
        answer_tb as at
        left join issue_tb as it on it.issue_id = at.issue_id
    where
        issue_type = 'Career'
),
b as (
    select
        distinct author_id
    from 
        answer_tb as at
        left join issue_tb as it on at.issue_id = it.issue_id
    where
        issue_type='Education'
        and author_id in (select * from a)
)
select count(b.author_id) as num from b