WITH RECURSIVE

gistfile1.rb

require 'spec_helper'

describe 'WITH RECURSIVE' do

  # http://www.postgresql.org/docs/8.4/static/queries-with.html
  # http://www.cybertec.at/common-mistakes-union-vs-union-all/

  def query(n)
    ActiveRecord::Base.connection.exec_query(
      <<-SQL
      WITH RECURSIVE one_to_inf(n) AS (
        VALUES (1)
      UNION ALL
        SELECT n+1 FROM one_to_inf
      ),
      take AS (
        SELECT n FROM one_to_inf LIMIT #{n}
      )
      SELECT sum(n)
      FROM take
      SQL
    )
  end

  it "(1..(1.0/0.0)).take(100).sum" do
    expect(
      query(100).to_hash
    ).to eq([
      { "sum" => "5050" },
    ])
  end
end