title: Filtering on activerecord relation without additional sql query?
body: <p>How do I filter the results of a AR query without executing an additional query?</p>
  
  <p>e.g.</p>
  
  <pre><code>u = User.where(name: "bob", age: [10, 20])
  # 1st select query to db
  u.class # ActiveRecord::Relation
  tens = u.where(age: 10)
  # 2nd select query to db
  </code></pre>
  
  <p>I don't want the second query to call the db, but rather filter on the results retrieved in u (1st query).</p>