题解 | #话题的分布情况#
话题的分布情况
https://www.nowcoder.com/practice/3f0d5c83b48b450888921b6189be288f
select substring_index(subject_set,',',1) as subject_id1, count(*) as cnt from comment_detail where substring_index(substring_index(subject_set,',',2),',',-1)=1002 group by subject_id1 order by subject_id1 asc;
注意substring_index的第三个参数如果是正数，表示从开头到中间的这部分
如果是负数，则表示中间到结尾的部分。
