我会用ar写如下：

class Category < ApplicationRecord
  scope :first_in_locale, ->() {
    joins(<<-SQL)
      JOIN (SELECT locale, min(id) AS id FROM categories GROUP BY locale) b ON b.id = categories.id
    SQL
    .select('categories.*')
    .order('categories.id')
  }
end

在rails控制台中：

2.5.1 :010 > pp Category.first_in_locale
  Category Load (0.9ms)  SELECT categories.* FROM "categories" JOIN (SELECT locale, min(id) as id from categories group by locale) b on b.id = categories.id ORDER BY categories.id
[#<Category:0x00007fc597e3db68
  id: 1,
  name: "Sociability",
  locale: "en",
  created_at: Sun, 16 Sep 2018 07:47:34 UTC +00:00,
  updated_at: Sun, 16 Sep 2018 07:47:34 UTC +00:00>,
 #<Category:0x00007fc597e3d3e8
  id: 3,
  name: "社會性",
  locale: "zh-TW",
  created_at: Sun, 16 Sep 2018 07:47:34 UTC +00:00,
  updated_at: Sun, 16 Sep 2018 07:47:34 UTC +00:00>]

下面是我用activerecord方式 Package 的sql答案。