title: Is there documentation for the Rails column types?
body: <p>I'm looking for more than the simple type listing <a href="http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/TableDefinition.html#method-i-column">that is found on this page</a>:</p>
  
  <blockquote>
    <p>:primary_key, :string, :text, :integer, :float, :decimal, :datetime, :timestamp, :time, :date, :binary, :boolean</p>
  </blockquote>
  
  <p>But is there any documentation that actually <em>defines</em> these fields?</p>
  
  <p>Specifically:</p>
  
  <ul>
  <li>What's the difference between <code>:string</code> and <code>:text</code>?</li>
  <li>Between <code>:float</code> and <code>:decimal</code>?</li>
  <li>What are the distinguishing features of <code>:time</code>, <code>:timestamp</code>, and <code>:datetime</code>?</li>
  </ul>
  
  <p>Are the nuances of these types documented anywhere?</p>
  
  <p>EDIT: <strong>Points of DB-platform implementations are irrelevant to the question I'm trying to ask.</strong>  If, say, <code>:datetime</code> does not have a defined intended meaning in Rails documentation, then what do db-adapter-writers go by when choosing a corresponding column type?</p>