$comma_separated = implode(",", $projects); // This is a comma-separated list of associated project ids.
$sql = "update tt_clients set name = ".$mdb2->quote($name).", address = ".$mdb2->quote($address).
", tax = $tax, projects = ".$mdb2->quote($comma_separated).", status = $status".
$comma_separated = implode(",", $projects); // This is a comma-separated list of associated project ids.
$sql = "update tt_clients set name = ".$mdb2->quote($name).", address = ".$mdb2->quote($address).
", tax = $tax, projects = ".$mdb2->quote($comma_separated).", status = $status".