How to build a shortcode which can insert a query string into a DB table

I need to build a landing page from which I can grab a token from a query-string in the URL.

I would therefore like to create a shortcode which can achieve this.

I have found a plugin which can grab the token and display it on the page. It looks like this:

add_shortcode("urlparam", "urlparam");
add_shortcode("ifurlparam", "ifurlparam");

function urlparam($atts, $content) {
    $defaults = array(
        'param'          => '',
        'default'        => '',
        'dateformat'     => '',
        'attr'           => '',
        'htmltag'        => false,
    );

    /* We used to use shortcode_atts(), but that would nuke an extra attributes
       that we don't know about but want. array_merge() keeps them all. */
    $atts = array_merge($defaults, $atts);

    $params = preg_split('/\,\s*/',$atts['param']);

    $return = false;

    foreach($params as $param)
    {
        if(!$return and ($rawtext = $_REQUEST[$param]))
        {
            if(($atts['dateformat'] != '') && strtotime($rawtext))
            {
                $return = date($atts['dateformat'], strtotime($rawtext));
            } else {
                $return = esc_html($rawtext);
            }
        }
    }

    if(!$return) {
        $return = $atts['default'];
    }

    if($atts['attr']) {
        $return = ' ' . $atts['attr'] . '="' . $return . '" ';

        if($atts['htmltag']) {
            $tagname = $atts['htmltag'];

            foreach(array_keys($defaults) as $key) {
                unset($atts[$key]);
            }

            $otheratts = "";
            foreach($atts as $key => $val) {
                $otheratts .= " $key=\"$val\"";
            }

            $return = "<$tagname $otheratts $return".($content ?
                    ">$content</$tagname>" : "/>");
        }
    }

    return $return;
}

/*
 * If 'param' is found and 'is' is set, compare the two and display the contact if they match
 * If 'param' is found and 'is' isn't set, display the content between the tags
 * If 'param' is not found and 'empty' is set, display the content between the tags
 *
 */
function ifurlparam($atts, $content) {
    $atts = shortcode_atts(array(
                               'param'           => '',
                               'empty'          => false,
                               'is'            => false,
                           ), $atts);

    $params = preg_split('/\,\s*/',$atts['param']);

    foreach($params as $param)
    {
        if($_REQUEST[$param])
        {
            if($atts['empty'])
            {
                return '';
            } elseif(!$atts['is'] or ($_REQUEST[$param] == $atts['is'])) {
                return do_shortcode($content);
            }
        }
    }

    if ($atts['empty'])
    {
        return do_shortcode($content);
    }

    return '';
}

I would like to add some code which puts the query string from the code above into my MySQL database. On https://www.w3schools.com/php/php_mysql_insert.asp I found this code:

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDBPDO";

try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username,
                    $password);
    // set the PDO error mode to exception
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $sql = "INSERT INTO MyGuests (firstname, lastname, email) VALUES ('John', 'Doe', '[email protected]')";
    // use exec() because no results are returned
    $conn->exec($sql);
    echo "New record created successfully";
}
catch(PDOException $e)
{
    echo $sql . "<br>" . $e->getMessage();
}

$conn = null;
?>

I therefore tried to combine the code by first creating a table with phpmyadmin called wp_token and afterwards inserting the line

$sql = "INSERT INTO wp_token ('$return')";

into the plugin code as can be seen below:

<?php
/*
Plugin Name: URL Params
Plugin URI: http://asandia.com/wordpress-plugins/urlparams/
Description: Short Code to grab any URL Parameter
Version: 2.1
Author: Jeremy B. Shapiro
Author URI: http://www.asandia.com/
*/

/*
URL Params (Wordpress Plugin)
Copyright (C) 2011-2016 Jeremy Shapiro

*/

//tell wordpress to register the shortcodes
add_shortcode("urlparam", "urlparam");
add_shortcode("ifurlparam", "ifurlparam");

function urlparam($atts, $content) {
    $defaults = array(
        'param'          => '',
        'default'        => '',
        'dateformat'     => '',
        'attr'           => '',
        'htmltag'        => false,
    );

    /* We used to use shortcode_atts(), but that would nuke an extra attributes 
       that we don't know about but want. array_merge() keeps them all. */
    $atts = array_merge($defaults, $atts);

    $params = preg_split('/\,\s*/',$atts['param']);

    $return = false;

    foreach($params as $param)
    {
        if(!$return and ($rawtext = $_REQUEST[$param]))
        {
            if(($atts['dateformat'] != '') && strtotime($rawtext))
            {
                $return = date($atts['dateformat'], strtotime($rawtext));
            } else {
                $return = esc_html($rawtext);
            }
        }
    }

    if(!$return) {
        $return = $atts['default'];
    }

    if($atts['attr']) {
        $return = ' ' . $atts['attr'] . '="' . $return . '" ';

        if($atts['htmltag']) {
            $tagname = $atts['htmltag'];

            foreach(array_keys($defaults) as $key) {
                unset($atts[$key]);
            }

            $otheratts = "";
            foreach($atts as $key => $val) {
                $otheratts .= " $key=\"$val\"";
            }

            $return = "<$tagname $otheratts $return".($content ?
                    ">$content</$tagname>" : "/>");
        }
    }

    $sql = "INSERT INTO wp_token ('$return')";

    return $return;
}

/*
* If 'param' is found and 'is' is set, compare the two and display the contact if they match
* If 'param' is found and 'is' isn't set, display the content between the tags
* If 'param' is not found and 'empty' is set, display the content between the tags
*
*/
function ifurlparam($atts, $content) {
    $atts = shortcode_atts(array(
                               'param'           => '',
                               'empty'          => false,
                               'is'            => false,
                           ), $atts);

    $params = preg_split('/\,\s*/',$atts['param']);

    foreach($params as $param)
    {
        if($_REQUEST[$param])
        {
            if($atts['empty'])
            {
                return '';
            } elseif(!$atts['is'] or ($_REQUEST[$param] == $atts['is'])) {
                return do_shortcode($content);
            }
        }
    }

    if ($atts['empty'])
    {
        return do_shortcode($content);
    }

    return '';
}

?>

However, it is not working. I am not sure if I need to define the connection first or what the issue is?