这样一个需求：
有一张表，里面有video_id,user_id,hashtag等字段。hashtag有大小写，现在需要将数据行聚集到某一hashtag中，且这个hashtag为数据表中同一hashtag(不区分大小写的hashtag)出现次数最多的。
原始数据表
| video_id | user_id | hashtag |
| --------------- | --------------- | --------------- |
| id_1 | uid_1 | happy |
| id_2 | uid_2 | Happy |
| id_3 | uid_3 | Happy |
Happy这个hashtag出现得最多，所以需要将所有不区分大小写的happy hashtag 都换成 Happy，然后聚合在一个。
中间表
| video_id | user_id | hashtag |
| --------------- | --------------- | --------------- |
| id_1 | uid_1 | Happy |
| id_2 | uid_2 | Happy |
| id_3 | uid_3 | Happy |
结果表
| hashtag | video_items | cnt |
| --------------- | ------------------------------ | --------------- |
| Happy | [{"video_id":"id_1", "user_id":| 3|
| | "uid_1", "hashtag":"Happy"}, | |
| | {"video_id":"id_2", "user_id":| |
| | "uid_2", "hashtag":"Happy"}, | |
| | {"video_id":"id_3", "user_id":| |
| | "uid_3", "hashtag":"Happy"},] | |