title: Rails - index for a query over three table columns
body: <p>I've got a query that I use often:</p>
  
  <pre><code>Site.where("mobile_visible = true AND (created_at &gt; :date OR updated_at &gt; :date)", :date =&gt; "12-04-30")
  </code></pre>
  
  <p>It produces this sql</p>
  
  <pre><code>SELECT `sites`.* FROM `sites` WHERE (mobile_visible = true AND (created_at &gt; '12-04-30' OR updated_at &gt; '12-04-30'))
  </code></pre>
  
  <p>I want to add an index or indexes to make this query more efficient.  Should I add 3 indexes for the 3 columns separately or 1 index indexing all three columns separately?</p>