Original update query

gistfile1.php

$updQuery = "UPDATE currentQueue SET ";
if (isset($_GET["arrive"]) && $_GET["arrive"] != "") {
  $updQuery .= "arrive=" . $arrive;
}
if (isset($_GET["depart"]) && $_GET["depart"] != "") {
  if (isset($_GET["arrive"]) && $_GET["arrive"] != "") {
    $updQuery .= ", ";
  }
  $updQuery .= "depart=" . $depart;
}

update.php

<?php

$db_params = new stdClass();
  $db_params->host = "localhost";
  $db_params->user = "Matt";
  $db_params->pass = "";
  $db_params->database = "parks";

$db = new mysqli($db_params->host,
                 $db_params->user,
                 $db_params->pass,
                 $db_params->database);

if (mysqli_connect_errno()) {
  die("Failed to connect to MySQL: " . $db->error);
}

if(!isset($_GET["id"]) || $_GET["id"] == "") {
  die("Missing id GET param.");
} else{
  $id = $_GET["id"];
}

if((!isset($_GET["arrive"]) || $_GET["arrive"] == "") && (!isset($_GET["depart"]) || $_GET["depart"] == "")) {
  die("Missing arrive and depart GET params.");
} else{
  if (isset($_GET["arrive"]) && $_GET["arrive"] != "") {
    $arrive = $_GET["arrive"];
  }
  if (isset($_GET["depart"]) && $_GET["depart"] != "") {
    $depart = $_GET["depart"];
  }
}

$updQuery = "UPDATE currentQueue SET ";
if (isset($_GET["arrive"]) && $_GET["arrive"] != "") {
  $updQuery .= "arrive=" . $arrive;
  if (isset($_GET["depart"]) && $_GET["depart"] != "") {
    $updQuery .= ", depart=" . $depart;
  }
} else if (isset($_GET["depart"]) && $_GET["depart"] != "") {
  $updQuery .= "depart=" . $depart;
}

$updQuery .= " WHERE id=" . $_GET["id"];

$stmt = $db->prepare($delQuery);

$execOutput = $stmt->execute();

$stmt->close();
$db->close();