خطا در هنگام اجرای دستورات PHP

[moseland]

<?php

$connect = mysql_connect('localhost','root','');

mysql_select_db('dbshare',$connect);

if (!isset($_POST['user']))

 exit();

$user = $_POST['user'];

$pass = $_POST['pass'];

$user = trim($user);

$sql="SELECT 'password'

 FROM 'users'

 WHERE 'username'= '$user'";

 

$result=mysql_query($sql);

if( mysql_num_rows($result)==1 && mysql_result($result,0)==$pass)

{

 header("location:admin.php");

}

else

{

 die("THE Username and/or password is incorrect !");

}

?>