Question

我遇到了一个小问题，现在我无法修复^ _ ^并希望看到你的建议。问题只是从mysql表中获取最新更新的几条记录。这是样本数据，但真实数据有数千条记录。

Id  site_id      updated_at               value
1   1            "2012-05-14 09:04:02"    5
2   2            "2012-05-14 09:04:02"    8
3   2            "2012-05-15 09:04:02"    9
4   3            "2012-05-16 09:04:02"    7
5   1            "2012-05-17 09:04:02"    5
6   1            "2012-05-18 09:04:02"    3

我想拥有将返回的XXXX功能

Id  site_id      updated_at               value
6   1            "2012-05-18 09:04:02"    3
4   3            "2012-05-16 09:04:02"    7
3   2            "2012-05-15 09:04:02"    9

Answer 1

这样的东西？

YourModel.order("updated_at desc").limit(3)

Answer 2

假设您的模型被称为Account：

Account.joins("LEFT OUTER JOIN accounts a 
    ON a.site_id = accounts.site_id AND a.value > accounts.value").
  where("a.value IS NULL").order("accounts.updated_at DESC").limit(3)

Active Record查询最新更新记录

2 个答案: