using WPDB to display external database-data inside a WP-shortcode - database

Question

I'm trying to figure out a way to use WPDB to load a whole row or single cells/fields from another table (not the Wordpress-DB) and displaying them in a shortcode. I have a bunch of weatherdata-values, I need the latest row (each column is another data-type (temp, wind, humidity, etc) of the database for a start.
Sadly, the plugin that would do everything that I need, SQL Shortcode, doesn't work anymore. I found this now:
https://de.wordpress.org/plugins/shortcode-variables/
Though I still need to use some PHP/PDO-foo to get the data from the database.
By heavy copy&pasting I came up with this:
<?php
$hostname='localhost';
$username='root';
$password='';
$dbname='sensordata';
$result = $db->prepare(SELECT * FROM `daten` WHERE id=(SELECT MAX(id) FROM `daten`););
$result->execute();
while ($row = $result->fetch(PDO::FETCH_ASSOC))
{
$data = $row['*'];
}
echo $data;
?>
But obviously it's not working. What I need to get it done with WPDB?
kind regards :)

Answer 1

Just in case anyone else needs this in the future. I used this now:
//connect to the database
<?php
$dbh = new PDO('mysql:host=localhost;dbname=databasename', 'dbuser',
'dbpasswort');
//query the database "databasename", selecting "columnname" from table "tablename", checking that said column has no NULL entry, sort it by column "id" (autoincrementing numeric ID), newest first and just fetch the last one
$sth = $dbh->query("SELECT `columnname` FROM `tablename` WHERE `columnname` IS NOT NULL order by id desc limit 1")->fetchColumn(0);
//print the value/number
print_r($sth);
?>
By using "SELECT colum1, colum2,... FROM" You should get all the columns, could be that fetchColumn needs to be replaced with something different though.