title: Notice: Undefined index $_POST and mysql
body: <p>If I set</p>
  
  <pre><code>$USER = (isset($_POST['username']));
  </code></pre>
  
  <p>with php have 0 errors <strong>BUT</strong> in db put '1' instead the it to user write on HTML input and if I put </p>
  
  <pre><code>`$USER = $_POST['username'];`
  
  Notice: Undefined index: username in __FILE__ on line 5
  </code></pre>
  
  <p>this set in the db what user put in the HTML input, but get error</p>
  
  <p>(Sorry for my bad English; I know it is so bad!)</p>