group by with first

example.rb

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"
  gem "rails", '6.0.0.rc2'
  # gem "rails", '6.0.0.rc1'
  # gem "rails", '6.0.0.beta1'
  # gem "rails", '5.2.3'
  gem 'pg'
end

require 'pg'
require "active_record"
require 'active_support'
require "minitest/autorun"
require "logger"

ActiveRecord::Base.establish_connection(adapter: "postgresql", database: "penseo_test2")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
    t.timestamps(null: false)
  end
end

class Post < ActiveRecord::Base
end

class BugTest < Minitest::Test
  def test_fails_with_distinct_size
    post = Post.create!

    expected = post.created_at
    assert_equal expected, Post.select('min(created_at) as min').reorder('').to_a.first.min
    assert_equal expected, Post.select('min(created_at) as min').reorder('').first.min
  end
end