relation.rb

class MyRelation
  def initialize(page)
    @page = page.to_i
    @limit = 10
  end

  def current_page
    @page
  end

  def total_pages
    res = execute(to_count_sql)
    total = res.getvalue(0, 0)
    (total.to_f / @limit).ceil
  end

  def limit_value
    @limit
  end

  def offset
    (@page - 1) * @limit
  end

  def all
    execute(to_sql)
  end

  def execute(sql)
    PG.connect(...).exec(sql)
  end

  def to_sql
    <<-SQL.strip_heredoc
    select distinct on (applicant_number) applicant_number, created_at, account_id from sms_messages
    where account_id = 147
    order by applicant_number, created_at DESC
    limit #{@limit} offset #{offset}
SQL
  end

  def to_count_sql
    "select count(distinct applicant_number) from sms_messages where account_id = 147"
  end
end