select substring_index (subject_set, ',', 1) subject_id1, count(*) cnt from comment_detail where substring_index ((substring_index (subject_set, ',', 2)), ',', -1) = '1002' group by subject_id1 order by subject_id1 题目不难,就是出题人说的不明白。这个题目想要查出第二个话题是'1002'对应的每一行数据的第一个话题的数目,很明显要gro...