title: What does ":" mean when using bindValue() in PHP PDO?
body: <p>What does <code>:</code> mean before <code>id</code> in the example below? Is it necessary?</p>
  
  <pre><code>$sth-&gt;bindValue(':id', $id, PDO::PARAM_INT);
  </code></pre>
  
  <p>Can I say <code>:id</code> is a variable?</p>
  
  <p>If <code>PDO::PARAM_INT</code> is not necessary, why would I need to use it?</p>