group-by.rb

require "active_record"

config = {
  adapter: "sqlserver",
  host: "localhost",
  port: 1433,
  username: "sa",
  password: "yourStrong(!)Password",
  database: "groupby"
}

class CreateUsers < ActiveRecord::Migration
  def change
    create_table :users do |t|
      t.string :role
    end
  end
end

class User < ActiveRecord::Base
end

ActiveRecord::Base.establish_connection config

unless ActiveRecord::Base.connection.data_source_exists? :users
  CreateUsers.new.change
  3.times do
    User.create(role: "member")
    User.create(role: "admin")
  end
end

p User.group(:role)
p User.group(:role).exists?