mysql group by 组内排序


有数据表 comments
------------------------------------------------
| id | newsID | comment | theTime |
------------------------------------------------
| 1  |        1      |         aaa    |     11       |
------------------------------------------------
| 2  |        1      |         bbb    |     12       |
------------------------------------------------
| 3  |        2      |         ccc     |     12       |

------------------------------------------------

newsID是新闻ID,每条新闻有多条评论comment,theTime是发表评论的时间

现在想要查看每条新闻的最新一条评论:


select * from comments group by newsID 显然不行


select * from comments group by newsID order by theTime desc 是组外排序,也不行


下面有两种方法可以实现:

(1)
selet tt.id,tt.newsID,tt.comment,tt.theTime from(  
select id,newsID,comment,theTime from comments order by theTime desc) as tt group by newsID 


(2)
select id,newsID,comment,theTime from comments as tt group by id,newsID,comment,theTime having
 theTime=(select max(theTime) from comments where newsID=tt.newsID)

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