title: how to compare/validate sql schema
body: <p>I'm looking for a way to validate the SQL schema on a production DB after updating an application version. If the application does not match the DB schema version, there should be a way to warn the user and list the changes needed.</p>
  
  <p>Is there a tool or a framework (to use programatically) with built-in features to do that?
  Or is there some simple algorithm to run this comparison?</p>
  
  <blockquote>
    <p><strong>Update:</strong> Red gate lists "from $395". Anything free? Or more foolproof than just keeping the version number?</p>
  </blockquote>