如何用php验证注册表单

我有四个页面分别是eq.php,re.php,login.php和register1.php
eq.php内容是
<?
require_once('login.php');

$link = mysql_connect("localhost","root","");

mysql_select_db("php");

$username=$_POST['username'];
$password=$_POST['password'];

$exec="select * from user where username='".$username."'";
if($result=mysql_query($exec))
{
if($rs=mysql_fetch_object($result))
{
if($rs->password==$password)
{
echo "<script>alert('Login Successful!');location.href='login.php';</script>";
}
else
{
echo "<script>alert('Password Wrong!');location.href='login.php';</script>";
}
}
else
{
echo "<script>alert('Username No Exist!');location.href='

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