我已经看到很多关于此类问题的解决方案(尤其是这个 SQL Select only rows with Max Value on a Column )，但这些似乎都不合适:
我有以下表格布局，附件的版本控制，绑定(bind)到实体:
TABLE attachments
+------+--------------+----------+----------------+---------------+
| id | entitiy_id | group_id | version_number | filename |
+------+--------------+----------+----------------+---------------+
| 1 | 1 | 1 | 1 | file1-1.pdf |
| 2 | 1 | 1 | 2 | file1-2.pdf |
| 3 | 1 | 2 | 1 | file2-1.pdf |
| 4 | 2 | 1 | 1 | file1-1.pdf |
| 5 | 2 | 1 | 2 | file1-2.pdf |
| 6 | 2 | 3 | 1 | file3-1.pdf |
+------+--------------+----------+----------------+---------------+
输出应该是最大版本号，按 group_id 和 entity_id 分组，如果有帮助，我只需要单个 entity_ids 的列表:
+------+--------------+----------+----------------+---------------+
| id | entitiy_id | group_id | version_number | filename |
+------+--------------+----------+----------------+---------------+
| 2 | 1 | 1 | 2 | file1-2.pdf |
| 3 | 1 | 2 | 1 | file2-1.pdf |
| 5 | 2 | 1 | 2 | file1-2.pdf |
| 6 | 2 | 3 | 1 | file3-1.pdf |
+------+--------------+----------+----------------+---------------+
我想出的是这个自连接:
SELECT *
FROM `attachments` `attachments`
LEFT OUTER JOIN attachments t2
ON ( attachments.group_id = t2.group_id
AND attachments.version_number < t2.version_number )
WHERE ( t2.group_id IS NULL )
AND ( `t2`.`id` = 1 )
GROUP BY t2.group_id
但是这个只有在不同的实体不共享相同的组号时才有效。不幸的是，这是必要的。
我在创建 View 时遇到了一个可行的解决方案，但我当前的设置不支持它。
任何想法都将受到高度赞赏。谢谢!
最佳答案
试试这个:
select t1.* from attachments t1
left join attachments t2
on t1.entity_id = t2.entity_id and t1.group_id = t2.group_id and
t1.version_number < t2.version_number
where t2.version_number is null
关于mysql - 选择最大值按两列分组的行，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/9360078/