题解 | 另一种分组计算思路

我觉得理解一下这句话“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”，无论是正向集合筛选逻辑还是反向集合筛选逻辑都可以，那这么理解就更好理解了，相当于两个韦恩图的交集嘛，那直接分组计算不就得了：

• 即回答过教育且回答了职场的用户数量（筛选回答教育或职场问题类型后，分用户组、回答问题的类型数>=2）

select
    count(distinct author_id) as num
from (
    select
        author_id,
        count(distinct issue_type) as answer_type_num
    from issue_tb as At1
    left join answer_tb as At2 using(issue_id)
    where issue_type in ("Education","Career")
    group by author_id
    having answer_type_num>=2
) as t1