<?php
session_start();

if(isset($_SESSION['sig']))
{
#User is already logged in
echo("<script>window.location='home.php'</script>");
}

if(isset($_REQUEST['submit'])
{
   #Perform login action
   $username=$_REQUEST['UserUsername'];
   $password=$_REQUEST['UserPassword'];

   include ('db_login.php');
   $query=mysql_query("SELECT * FROM Users WHERE UserUsername='".$username."' AND UserPassword='".$password."'");
   $row=mysql_fetch_arr($query);
   if(empty($row))
     {
        #False Info / User doesn't exist
        echo('<script>alert("False login credentials!");</script'));
     }
     else
     {
         #User exists and login is successful
         $_SESSION['sig']="OK";
     }

  }

?>