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#

# c查询职场用户
select
  count(distinct ab1.author_id) num
from
  answer_tb ab1
  inner join (
    select
      ab.author_id
    from
      issue_tb it
      inner join answer_tb ab on it.issue_id = ab.issue_id
    where
      it.issue_type = "Education"
  ) M on M.author_id = ab1.author_id
  inner join issue_tb it1 on it1.issue_id = ab1.issue_id
where
  it1.issue_type = "Career"