每个线程选择最新消息

Question

我有一个表格（消息），其中包含以下列

message_id（ pk ），thread_id，message_body，date_posted，posted_by，....

如何根据date_posted选择每个线程的最新消息，结果按降序排列？

样本表

-------------------------------------------------
message_id  |  thread_id  |  body |  date_posted  
-------------------------------------------------
1           |  1          |  ...  |  2016-06-03
-------------------------------------------------
2           |  1          |  ...  |  2016-06-04
-------------------------------------------------
3           |  2          |  ...  |  2016-06-05
-------------------------------------------------
4           |  1          |  ...  |  2016-06-06
-------------------------------------------------
5           |  2          |  ...  |  2016-06-07
-------------------------------------------------
6           |  3          |  ...  |  2016-06-08
-------------------------------------------------
7           |  2          |  ...  |  2016-06-09
-------------------------------------------------

预期结果

-------------------------------------------------
message_id  |  thread_id  |  body |  date_posted  
-------------------------------------------------
7           |  2          |  ...  |  2016-06-09
-------------------------------------------------
6           |  3          |  ...  |  2016-06-08
-------------------------------------------------
4           |  1          |  ...  |  2016-06-06
-------------------------------------------------

Answer 1

试试这个;）

select t1.*
from messages t1
inner join (
    select max(date_posted) as date_posted, thread_id
    from messages
    group by thread_id
) t2 on t2.thread_id = t1.thread_id and t2.date_posted = t1.date_posted
order by t1.date_posted

或者您可以使用in：

select *
from messages
where (date_posted, thread_id) in (
    select max(date_posted) as date_posted, thread_id
    from messages
    group by thread_id
)
order by date_posted

SQLFiddle DEMO HERE

Answer 2

你可以这样做

SELECT thread_id,message FROM  (Select *  from messages   ORDER BY thread_id,latestDate DESC) r group by thread_id;

Answer 3

试试这个

SELECT * FROM messages GROUP BY thread_id ORDER BY  date_posted DESC;

Answer 4

通过以降序为基础给出基于thread_id和date_posted的行号，只是另一个视角。

<强>查询

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SQL Fiddle Demo