Select 多列但仅按 1 列分组

Question

我有评论table

我需要获取计数，comment_id，以及最新的 when_added

comment_id	when_added	count
10	02/24/2022	2
21	02/23/2022	1

我试过这个查询

SELECT COUNT(*) as count, comment_id, when_added 
FROM comment 
GROUP BY comment_id, when_added 
ORDER BY when_added DESC;

有没有办法只用comment_id分组？

Answer 1

您应该仅按 comment_id 分组，并使用 MAX() 聚合函数为每个 comment_id 获取最后一个 when_added：

SELECT comment_id, 
       MAX(when_added) last_when_added, 
       COUNT(*) count
FROM comment 
GROUP BY comment_id 
ORDER BY last_when_added DESC;

Select multiple columns but group by only 1 column