Live check availability using PHP

today am going to learn trick on live check availability   .Before going to learn u need to have some grip on database management,PHP.
so get ready to learn 1
                      2
                      3
                      Lets go.................

whatever you are going to enter text(email id) 

u get the text and check with the database data.php code for checking

<?phpinclude 'database.php';
if(isSet($_POST['username'])

{$sql=mysql_query('SELECT * FROM registration'); 

while($row=mysql_fetch_array($sql)){$get=$row['regusername'];$p=$_POST['username'];if($p==$get)echo "<big><font color='RED'>Not available";elseecho "<big><font color='green'>Available";}}?>

DATABASE CONNECTION :

<?phpmysql_connect("localhost","USERNAME","PASSWORD");mysql_select_db("DATABASE NAME");?>

HTML CODE :

<style>
#main
{
margin-left:275;
width:600px;
padding:10px;
border:solid 1px blue;
background:#eeeeee;
}
</style>
<div id="main">
<b>Already  'vydyas@gmail.com' is existed so if u check with another u can identify<br>
               is it working or not
<form id='myform' method='POST' action='index.php' enctype="multipart/form-data">
<input type='text' name='username' size=15>
<button>check</button>
</form>


<?php

include 'result.php';
?>