title: PHP - MySQL error "Error: Query was empty" when someone tries to sign up with a username that is already taken
body: <p>I've got a signup/login system on my site, and I've made it so that if someone tries to sign up with a username that is already in use, it posts an error underneath the form. However, instead of posting the error message that I created, it returns a MySQL error "Error: Query was empty". Here is the code that I am trying to use to do this:</p>
  
  <pre> // checks if the username is in use
    if (!get_magic_quotes_gpc()) {
     $_POST['username'] = addslashes($_POST['username']);
    }
   $usercheck = $_POST['username'];
   $check = mysql_query("SELECT username FROM userpass WHERE username = '$usercheck'") 
   or die(mysql_error());
   $check2 = mysql_num_rows($check);
  
   //if the name exists it gives an error
   if ($check2 != 0) {
     $error = "Sorry, the username ".$_POST['username']." is already in use.";
       }</pre>
  
  <p>What am I doing wrong?</p>
  
  <p>Thanks</p>