is deze $_GET veilig?

<?PHP

function check_key ($key)
{
    return ereg ("([a-z0-9])$", $key) ? TRUE : FALSE;
}

if (isset ($_GET['key']))
{
    if (check_key ($_GET['key']))
    {
        //query
    }
}
?>

<?PHP
 
function check_key ($key)
{
    return ereg ("([a-z0-9])$", $key) ? TRUE : FALSE;
}
 
if (isset ($_GET['key']))
{
    if (check_key ($_GET['key']))
    {
        //query
    }
}
?>

return (!empty($key) || ctype_alnum($key))

return (!empty($key) || ctype_alnum($key))

return ereg ("^[a-z0-9]*$", $key)

return ereg ("^[a-z0-9]*$", $key)