MySQL-连接表，仅检索最大ID [英] MySQL - Join tables, retrieve only Max ID

问题描述

我在其他帖子上也看到了类似问题的解决方案，但是在将其应用于我的特定问题时遇到了问题.

I've seen solutions for something similar on other posts, but I've been having an issue applying it to my specific problem.

这是我的初次加入:

SELECT service_note_task, comment_id, comment FROM service_note_task LEFT JOIN service_note_task_comments ON service_note_task.service_note_task_id = service_note_task_comments.service_note_task_id;  

这将导致:

+-----------------------------+------------+--------------+
| service_note_task           | comment_id | comment      |
+-----------------------------+------------+--------------+
| This is service note task 3 |         25 | Comment      |
| This is service note task 3 |         26 | Comment Blah |
| This is service note task 3 |         36 | aaa          |
| This is service note task 2 |         13 | Awesome comm |
| This is service note task 1 |         12 | Cool Comm    |
+-----------------------------+------------+--------------+

但是对于每个service_note_task，我实际上只需要一行代表具有最高comment_id的注释，就像这样:

But for each service_note_task, I really only need one row representing the comment with the highest comment_id, like this:

+-----------------------------+------------+--------------+
| service_note_task           | comment_id | comment      |
+-----------------------------+------------+--------------+
| This is service note task 3 |         36 | aaa          |
| This is service note task 2 |         13 | Awesome comm |
| This is service note task 1 |         12 | Cool Comm    |
+-----------------------------+------------+--------------+

我认为我可以在子选择语句中使用MAX来缩小结果的范围.如何将其合并到语句中以获得这些结果?

I figure I could use MAX in a sub-select statement to narrow down the results as I want them. How can I incorporate that into my statement to get these results?

推荐答案

作为参考，这称为"groupwise-maximum"

For reference, this is known as "groupwise-maximum"

http://dev. mysql.com/doc/refman/5.0/en/example-maximum-column-group-row.html

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