$keyword = trim($_GET["Keyword"]);

$url = "webpage.php?";
$url .= "&Keyword=$keyword";

$shopByStore = $_GET["store"];
if (!empty($shopByStore)) {
$url .= "&store=$shopByStore";
}
// with 7 more GET methods potentially retrieving values for the URL parameters

<a href="<?php echo $url; ?>">anchor text</a><br>

if (isset($_GET["store"])) {
$_SESSION["shopByStore"] = $_GET["store"];
}