oci8 error in DB.php

I'm getting an error too, though it is different,

Here it is:

Fatal error: Call to undefined function: query() in functions.php on line 70

Here is the code that causes the error, what is wrong?

function funcLogin($username, $password)
{
include './dbinfo.php';
require_once( 'DB.php' );

if(!$username || !$password)
 {
  $feedback .= 'User Name and Password are both required';
  return false;
 }else{
  $db = DB::connect( "oci8://$dbuser:$dbpass@$dbhost/$dbname");

   $sql = "SELECT * FROM rusers where username = '$username' AND
password='". md5($password) ."';

if ( DB::isError( $doesUserExist = $db->query( $sql ) ) )
   {
    echo DB::errorMessage($doesUserExist);
   }else{
     // output results of query into $resultRow Array
    // other code not related to problem at hand........