mysql group by组内排序

mysql group by组内排序

 

有数据表 comments

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| id | newsID | comment | theTime |

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| 1  |        1      |         aaa    |     11       |

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| 2  |        1      |         bbb    |     12       |

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| 3  |        2      |         ccc     |     12       |

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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：

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（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)