title: Is using COUNT(*) or SELECT * a good idea?
body: <p>I've heard several times that you shouldn't perform <code>COUNT(*)</code> or <code>SELECT *</code> for performance reasons, but wasn't able to dig up some further information about it.</p>
  
  <p>I can imagine that the database is then using <em>all</em> columns for the action, which can be an impressive performance loss, but I'm not sure about that. Does somebody have further information about the topic?</p>