title: How to prevent duplicate Usernames in php/mysql
body: <p>(This is my first try with php)</p>
  
  <p>I have a very basic register page.
  <a href="http://graves-incorporated.com/test_sites/member_test/register/register.php" rel="nofollow">http://graves-incorporated.com/test_sites/member_test/register/register.php</a></p>
  
  <p><em>*</em> I just remembered PHP code doesn't show up in the source so here it is:</p>
  
  <pre><code>enter code here
  &lt;?php
  include('connection.php');
  
  if(isset($_POST['form'])){
      if(empty($_POST['username']) || empty($_POST['password']) || empty($_POST['conf_pass']) || empty($_POST['email'])){
          echo '&lt;b&gt;Please fill out all fields.&lt;/b&gt;';
  
      }elseif($_POST['password'] != $_POST['conf_pass']){
          echo '&lt;b&gt;Your Passwords do not match.&lt;/b&gt;';
      }else{
          $url = 'http://graves-incorporated.com/test_sites/plantation_park_2012/';
          echo '&lt;META HTTP-EQUIV=Refresh CONTENT="2; URL='.$url.'"&gt;';
          echo '&lt;b&gt;Congrats, You are now Registered.&lt;/b&gt;';
          mysql_query("INSERT INTO users VALUES(NULL, '$_POST[username]', '$_POST[password]', '$_POST[email]')");     
      }
  }
  ?&gt;
  </code></pre>
  
  <p>I want to make sure I don't get duplicate users and/or email addresses in the database.  I set up a Unique Key in MySQL for Username and Email, which prevents it, but the user on the actual form doesn't know that, it still tells them "Congrats, you are signed up" or whatever it says... haha</p>
  
  <p>So what can I add to the php code (and where in the code) that would prevent this?</p>
  
  <p>Thanks for helping this major noob,
  Dan Graves</p>