נו בסדר אותו הדבר....
PHP קוד:
$SQL -> sql_query("SELECT * FROM tblname ORDER BY ID DESC LIMIT 1");
$SQL -> fetch_array( $SQL -> query);
$highestId = $SQL -> fetch['id'];
$checkResult = intval( $_GET['id']);
if( $checkResult > $highestId){
echo "Error";
}
else
{
echo "Result Are Ok";
}