title: exactly what does rake db:migrate do?
body: <p>Does rake db:migrate only add new migrations, or does it drop all migrations/changes and build everything new?</p>
  
  <p>I think rake is throwing an error because it is trying to access a table attribute in migration 040 that was deleted in migration 042. somehow my DB and rake are out of synch and I want to fix them.</p>
  
  <p>for you experts out there - is it common for rake to get out of synch with migrations? how can I avoid this (no, I do not hand-edit my schema or rake files).</p>