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
https://www.nowcoder.com/practice/b02cf9ee7b9f4cdda308f8155ff3415d
SELECT COUNT(DISTINCT author_id) AS num
FROM answer_tb JOIN issue_tb USING(issue_id)
WHERE issue_type = 'Education'
AND author_id IN
(
SELECT author_id
FROM answer_tb JOIN issue_tb USING(issue_id)
WHERE issue_type = 'Career'
)
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