title: Creating a PostgreSQL sequence to a field (which is not the ID of the record)
body: <p>I am working on a Ruby on Rails app. We are using a PostgreSQL database.</p>
  
  <p>There is a table named <code>scores</code> with the following columns: </p>
  
  <pre><code>Column        | Type
  --------------+-----------------------
  id            | integer
  value         | double precision
  ran_at        | timestamp
  active        | boolean
  build_id      | bigint
  metric_id     | integer
  platform_id   | integer
  mode_id       | integer
  machine_id    | integer
  higher_better | boolean
  job_id        | integer
  variation_id  | integer
  step          | character varying(255)
  </code></pre>
  
  <p>I need to add a <em>sequence</em> to <code>job_id</code> (note: there is no model for <code>job</code>).</p>
  
  <p>How do I create this sequence?</p>