Erreur PHP : Unknown column 'twitter' in 'field list'

<?php 

if(isset($_POST['submit']))
{

$twitter= htmlspecialchars(trim($_POST['twitter']));
$facebook= htmlspecialchars(trim($_POST['facebook']));
$google= htmlspecialchars(trim($_POST['google']));

$sql = "UPDATE covoiturage_users SET twitter='$twitter', facebook='$facebook', google='$google' WHERE username='".$_SESSION['username']."'";
	  $requete = mysql_query($sql) or die(mysql_error()); 
	
	echo('<div class="alert alert-success">
							<button type="button" class="close" data-dismiss="alert">×</button>
							<strong>Succès !</strong> Vos réseaux sociaux ont bien été enregistré.
						</div> <br>');	
	}?>


					<?php 	$sql = "SELECT * FROM covoiturage_users WHERE username='".$_SESSION['username']."'"; 
					$query = mysql_query($sql) or die(mysql_error());
					while($fetch = mysql_fetch_assoc($query)):
		
			?>


<div class="module">
<div class="module-header">
<h3>Modifications mes réseaux sociaux</h3>
</div> <!-- .module-header -->

<div class="module-content">

<div class="room-statuses-body">

<div id="timelinetable">
<div class="items">

<div class="span4" style="width:289px">
<form action="config-reseaux.php" name="login" method="post">
<fieldset><p>
<div class="control-group">
<img src="http://www.missesdressy.fr/images/front/twitter32.png" width="32" height="32"> &nbsp Twitter<br><br>
<div class="input-prepend">
<span class="add-on">https://twitter.com/</span>
<input  type="text" class="span3" name="twitter" id="twitter" placeholder="Nom d'utilisateur" value="<?php echo $fetch['twitter']; ?>" />
</div>
</div>
<br><br>
<div class="control-group">
<img src="http://l.yimg.com/a/i/de/facebook-icon-32.png" width="32" height="32"> &nbsp Facebook<br><br>
<div class="input-prepend">
<span class="add-on">https://www.facebook.com/</span>
<input  type="text" class="span3" name="facebook" id="facebook" placeholder="Nom d'utilisateur" value="<?php echo $fetch['facebook']; ?>" />
</div>
</div>
<br><br>
<div class="control-group">
<img src="https://www.u-cergy.fr/skins/Univ-Cergy/resources/img/google32.png" width="32" height="32"> &nbsp Google+<br><br>
<div class="input-prepend">
<span class="add-on">https://plus.google.com/</span>
<input  type="text" class="span3" name="google" id="google" placeholder="ID d'utilisateur" value="<?php echo $fetch['google']; ?>" />
</div>
</div>
<br><br>

<button class="btn btn-success" name="submit" type="submit">Enregistrer</button>
</p></fieldset>
</form>
</div>
<?php endwhile; ?>