如何用PHP调用不带参数的oracle函数？

$conn = oci_connect('username', 'password', 'hostname/service_name');
if (!$conn) {
    $e = oci_error();
    trigger_error(htmlentities($e['message'], ENT_QUOTES), E_USER_ERROR);
}

$sql = 'BEGIN function_name(); END;';
$stmt = oci_parse($conn, $sql);
if (!$stmt) {
    $e = oci_error($conn);
    trigger_error(htmlentities($e['message'], ENT_QUOTES), E_USER_ERROR);
}

$result = oci_execute($stmt);
if (!$result) {
    $e = oci_error($stmt);
    trigger_error(htmlentities($e['message'], ENT_QUOTES), E_USER_ERROR);
}

if (oci_fetch($stmt)) {
    $result = oci_result($stmt, 1); // 获取第一个列的值
    echo $result;
}

oci_free_statement($stmt);
oci_close($conn);