sql_paginator.rb

class AnyPage
  attr_reader :sql

  def initialize(sql, options = {})
    @page_size = options.fetch(:page_size) { 1000 }
    @sql = sql
    @total_pages = nil
  end

  def self.page(sql, nth, options = {})
    new(sql, options).page(nth)
  end

  def count
    @total_pages ||= begin
      statement = <<-SQL
        SELECT COUNT(*) FROM (#{sql}) as t
      SQL

      results = ActiveRecord::Base.connection.execute(statement)
      results.first["count"]
    end
  end

  def pages
    page_count = count / @page_size
    page_count < 1 ? 1 : page_count
  end

  def page(nth)
    nth = nth <= 0 ? 0 : nth - 1
    statement = <<-SQL
      SELECT * FROM (#{sql}) AS t
      LIMIT #{@page_size}
      OFFSET #{nth * @page_size}
    SQL

    ActiveRecord::Base.connection.execute(statement)
  end
end