I am using the code below to insert the username and password to keep thi id and password record
i want the change that if the id and password exist it replace the id and password in the database
$username=$_POST['login'];
$password=$_POST['passwd'];
$con=mysql_connect('localhost','root',''); //establishing connection with server
mysql_select_db("sql", $con); //selecting DataBase
mysql_query("INSERT INTO login (username, password)
VALUES ('$username', '$password')");