<?

$name = 'foo';
$age = '123';

if ($level != '') $fields[] .= "level = '" . mysql_escape_string($level) . "'";
if ($name != '')  $fields[] .= "name = '" . mysql_escape_string($name) . "'";
if ($age != '')   $fields[] .= "age = '" . mysql_escape_string($age) . "'";

if (!is_array($fields))
{
    // ...
}
else
{
    $query = "UPDATE users SET " . join(", ", $fields) . " WHERE id = 1";
    echo $query;
}


?>