如何在Javascript和PHP中更新mysql而无需在每个请求上启动新连接？

Question

I have some training videos in which I update the database once per second. The working code that I have passes seconds watched from JS to PHP to Mysql. The problem that I am having is that it will not update unless I start a new connection with every request (every second). Is there a better way? My JS code;

//AJAX save 'seconds played' values to database
function updatedb() {
if (window.XMLHttpRequest) { 
    xmlhttp = new XMLHttpRequest();
} else { 
    xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");}
xmlhttp.open("GET","http://localhost/userupdate.php?q=" + userID + "&r=" +     (medeno[index][0]) + "&s=" + index, true);
xmlhttp.send();
}

and my PHP code (seperate file.php);

<?php

//Get values
$userID=$_GET['q'];
$secc=$_GET['r'];
$index=$_GET['s'];

$userID=(int)$userID;
$secc=(int)$secc;
$index=(int)$index;

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$mysqli = new mysqli("localhost", "medeno_user", "cr3134", "medeno_users");


//Update database 1 case per video course
switch ($index) {
    case 1: $stmt1=$mysqli->prepare('UPDATE users set videoSec1=? WHERE     userID=?'); break;
    case 2: $stmt1=$mysqli->prepare('UPDATE users set videoSec2=? WHERE userID=?'); break;
    case 3: $stmt1=$mysqli->prepare('UPDATE users set videoSec3=? WHERE userID=?'); break;
    case 4: $stmt1=$mysqli->prepare('UPDATE users set videoSec4=? WHERE userID=?'); break;
    case 5: $stmt1=$mysqli->prepare('UPDATE users set videoSec5=? WHERE userID=?'); break;
    case 6: $stmt1=$mysqli->prepare('UPDATE users set videoSec6=? WHERE userID=?'); break;
    case 7: $stmt1=$mysqli->prepare('UPDATE users set videoSec7=? WHERE userID=?'); break;
    case 8: $stmt1=$mysqli->prepare('UPDATE users set videoSec8=? WHERE userID=?'); break;}

$stmt1->bind_param('ii',$secc,$userID);
$stmt1->execute();
$stmt1->close();