title: Double Hyphen/Dash in SQL-Injection. What are they used for?
body: <p>I'm currently learning how SQL-Injections work. On many teaching-websites there are examples shown, such as</p>
  
  <pre><code>SELECT fieldlist
  FROM table
  WHERE field = 'x' AND email IS NULL; --';
  </code></pre>
  
  <p>In the field 'field' the content thats going to be checked comes from a textfield or something similar from a website. The user-input in this case is <code>x' AND email IS NULL; --</code> 
  What is the use of <code>--</code> ??</p>
  
  <p>I saw a few similar examples but no explanation. Am I missing something fundamental?</p>