login.php

<?php
include("config.php"); 
function redirect($url) {
    ob_start();
    header('Location: '.$url);
    ob_end_flush();
    die();
}
$link = mysql_connect($db_host, $db_user, $db_pass)
or die ("Could not connect to mysql because ".mysql_error());
mysql_select_db($db_name)
or die ("Could not select database because ".mysql_error());
$match = "select id from $db_table where username = '".$_POST['username']."'
and password = '".$_POST['password']."';"; 
$qry = mysql_query($match)
or die ("Could not match data because ".mysql_error());
$num_rows = mysql_num_rows($qry); 
if ($num_rows <= 0) { 
echo "Sorry, there is no username $username with the specified password.<br>";
echo "<a href=login.html>Try again</a>";
exit; 
} else {
session_start();
$username=$_POST['username'];
$_SESSION['login_user']=$username; 
$url="main_page.php";
redirect($url);
}
?>