<?php
     $username = $_POST['username']; //this is the username passed
   $password = $_POST['password']; //this is the password passed

   $checkQuery = "SELECT username, password FROM users WHERE username='$username' password='$password'";


   $checkQueryResult = mysql_query($checkQuery) or die(mysql_error());

   if ( mysql_num_rows($checkQueryResult >= 1) )
   {
      $_SESSION['username'] = $username;
   }
   else
   {
      echo "Login Credentials do not match."
   }
?>