题解 | SQL 193. 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 t1 AS (
    SELECT answer_date,
           author_id,
           b.issue_type
    FROM answer_tb a
    LEFT JOIN issue_tb b
    ON a.issue_id = b.issue_id
    ORDER BY answer_date,author_id
),
t2 AS (
    SELECT
        answer_date,
        author_id
    FROM t1
    WHERE issue_type = 'Education'
),
t3 AS (
    SELECT * FROM t1
    WHERE author_id IN
          (
              SELECT  author_id
              FROM t2
          ) AND issue_type = 'Career'
)
SELECT count(author_id) AS num FROM t3;

# 这道题细节是不需要考虑是否有时间先后顺序的类别！