title: How do I make a column unique and index it in a Ruby on Rails migration?
body: <p>I would like to make a column <code>unique</code> in Ruby on Rails migration script. What is the best way to do it? Also is there a way to index a column in a table?</p>
  
  <p>I would like to enforce <code>unique</code> columns in a database as opposed to just using <code>:validate_uniqueness_of</code>.</p>