题解 | #某乎问答高质量的回答中用户属于各级别的数量#

• 先筛选出回答数量大于等于100的
• 然后计算每个级别的回答数量（形成一个新表t1）
• 利用case when 语句，筛选出1-2级，3-4级，5-6级(level_cut)
• 最后group by level_cut,计算每个级别数量和

select 
	CASE
	WHEN author_level BETWEEN 1 and 2 THEN '1-2级'
    WHEN author_level BETWEEN 3 and 4 THEN '3-4级'
    ELSE '5-6级'
    END AS 'level_cut',
    sum(amount) as num
from
(select 
	author_level,
    count(char_len) as amount
from author_tb
join answer_tb
using(author_id)
where char_len>=100
group by author_level
order by author_level) t1
group by level_cut
order by num desc