title: Rails 4 Migration Error (Can't rake db:migrate) SQLite3::SQLException: duplicate column name
body: <p>I've been trying to get the Paperclip gem working. The problem that I was initially running into was that pictures were getting uploaded but not displaying. I then messed around with the database by doing a rake db:rollback to try and fix the error. Now I can't rake db:migrate again because of this error </p>
  
  <pre><code>SQLite3::SQLException: duplicate column name: image_file_name: ALTER TABLE "posts" ADD "image_file_name" varchar
  </code></pre>
  
  <p>I've personally went into the migration folder and deleted the file to try and generate a migration again. I've been trying to do rails generate paperclip post image and it does create a migration file, but I'm unable to rake db:migrate.</p>
  
  <p>Any suggestions?</p>
  
  <p>Thanks!</p>