Id  Username    Password
1   admin       admin
2   jay         jay1
3   suman       xyza
4   chintan     abcde

$fetchid = mysql_query(" SELECT MAX(Id) As max From user;");
$row = mysql_fetch_array($fetchid);
$largest = $row['max'];
$largest++;

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

$result = mysql_query(" INSERT INTO `proshell`.`user` (
`Id` ,
`Username` ,
`Password`
)"."
VALUES (
'".$largest."', '".$user."', '".$pass."'
);");