I'm trying to create a form for admin registration. The code works correctly but more than one admin can register for this page. How can I make it so that only one admin can register?
<html >
<head>
<title></title>
</head>
<body>
<?php
print ("<form action='admin.php' method='post'>
    <p>Name
        <input type='text' name='firstname'  />
    </p>
    <p>Surname
        <input type='text' name='lastname' />
    </p>
    <p>Username
        <input type='text' name='username' />
    </p>
    <p>Password
        <input type='password' name='password' />
        </p>
        <p>Email <input type='text' name='email'/>  </p>
      
      
    
  <input type='submit'  value='Register'/>  
</form>
        ");
if( !($database=mysql_connect("localhost","root",""))||!(mysql_select_db("st_login",$database))  )
   print("Could not connect");
if(isset($_POST['firstname'] )&&isset($_POST['lastname'])&&isset($_POST['username'])&&isset($_POST['password'])
  /*&&isset($_POST['notat'])&&isset($_POST['lendet'])*/&&isset($_POST['email'])){
$firstname=$_POST['firstname'];
$lastname=$_POST['lastname'];
$username=$_POST['username'];
$password=md5($_POST['password']);
$email=$_POST['email'];
/*
$notat=$_POST['notat'];
$lendet=$_POST['lendet'];
*/
$query = "INSERT INTO  login (firstname, lastname, username,password,email,admin) VALUES ('$firstname', '$lastname',
 '$username','$password','$email',1)";
}
if ( !empty($firstname)&&!empty($lastname)&&!empty($username) &&!empty($password)&&!empty($email))
{
  if(!($result=mysql_query($query,$database)))
{
    print("Could not execute query");
    die (mysql_error());//ose error
}
echo "YOU HAVE BEEN REGISTERED SUCCESSFULLY!You are the admin of this page";
}
else echo 'Fill in all the blank fields';
mysql_close($database);
?>
</body>
</html>
 
     
     
    