PHP script error Notice: Undefined variable
<p>I am writing a PHP script for advanced searching but an error occurred. Please help<br />
<strong>Code:</strong> </p>

<pre><code>$key    = $_GET['key'];
$auth   = $_GET['auth'];
$lang   = $_GET['lang'];
$pub    = $_GET['pub'];

if(isset($key) OR isset($auth) OR isset($lang) OR isset($pub))
{
    if ($key    != NULL){$keyword   = "AND (native_name LIKE '%".$key."%' OR unique_name LIKE '%".$key."%')";}
    if ($auth   != 0)   {$auther    = "AND auth_id=".$auth."";}
    if ($lang   != 0)   {$language  = "AND lang_id=".$lang."";}
    if ($pub    != 0)   {$publisher = "AND pub_id=".$pub."";}

    $search_query = "SELECT native_name from books WHERE status=1 ".$keyword." ".$auther." ".$language." ".$publisher."";
    print $search_query;
}
</code></pre>

<p><strong>Error:</strong><br /><br />
Notice: Undefined variable: keyword in FILE_PATH on line 90<br />
Notice: Undefined variable: auther in FILE_PATH on line 90<br />
Notice: Undefined variable: language in FILE_PATH on line 90<br />
Notice: Undefined variable: publisher in FILE_PATH on line 90</p>
