set pagination pagenumber as default url - php

Question

So i managed to build a working pagination system in php. But i want users to default to the first pagenumber of said pagination, so for example if somebody clicks on category 1 the URL will change to this website.php?category=1 i would like this to be website.php?category=1&pagenumber=1 as the default URL.
The reason why i want this is so i don't have to write 2 different query's: 1 if the category isset but no pagenumber, and 1 if both are set.
function getNews()
{
// check if category is get via URL
if (isset($_GET["category"]) && is_numeric($_GET["category"]) && intval($_GET["category"])) {
// bind get category to categoryId
$categoryId = intval($_GET["category"]);
// if category is 1
if ($categoryId == 1) {
try {
$db = new Connection();
$database = $db->openConnection();
if (isset($_GET["pagenumber"]) && is_numeric($_GET["pagenumber"]) && intval($_GET["pagenumber"])) {
$pageNumber = intval($_GET["pagenumber"]);
$itemsPerPage = 9;
$offset = ($pageNumber - 1) * $itemsPerPage;
$stm = $database->query("SELECT * FROM blog where blog.Categoryid = $categoryId LIMIT 9 OFFSET $offset ");
$stm->execute();
$rowNews = $stm->fetchAll(PDO::FETCH_ASSOC);
$totalItems = $database->query("SELECT COUNT(*) FROM blog where blog.Categoryid = $categoryId")->fetchColumn();
$totalPages = intval(ceil($totalItems / $itemsPerPage));
$previousButton = ($pageNumber + 1) - $totalPages;
$nextButton = ($pageNumber) * $totalPages;
$pageIndex = 0;
this is what i currently have(i cut out the pagination system, can paste it in if needed).
//
this is how i generate my category select
<?php
if (isset($_GET["category"])){
$db = new Connection();
$categoryId = $_GET["category"];
$database = $db->openConnection();
$stm = $database->query("SELECT * FROM category");
$stm->execute();
$fetchCategory = $stm->fetchAll(PDO::FETCH_ASSOC);
foreach ($fetchCategory as $cats) {
?>
<a class="dropdown-item" href="blog.php?category=<?php echo $cats["categoryid"]; ?>"><?php echo $cats["categorytitle"]; ?></a>
<?php
}
?>
<?php
}else{
$categoryId = 1;
}
?>
</div>
</div>
<?php
$categoryId = -1;
if (isset($_GET["category"]) && intval($_GET["category"])) {
$categoryId = intval($_GET["category"]);
switch ($categoryId) {
case 1:
// do query for category id 1
getNews();
break;
case 2:
// do query for category id 2
getEwarehouse();
break;
case 3:
// do query for category id 3
getPartners();
break;
default:
ifnotNumeric();
break;
}
} else {
ifnotSet();
}
?>
Some more general information:
Running laragon 4.0.15 with PHP 7.3.9
Using HeidiSQL 10.2.0.5599
Using PHPStorm 2019.2.2
if you need anymore code examples i can paste them in.