How Do I SELECT These Two Tables Using A Single PDO Query

I have two MySQL tables, which I want to SELECT using a single PDO query and positional placeholders.

I've been going through similar questions here to find a solution, but none seems to match the issues I'm having.

The following code is the section of my script:

<?php
// query users table to retrieve its contents   
if (isset($_SESSION["user_id"]["0"]))
{               
    // select a particular user by user_id
    $user_id = isset($_POST["user_id"]) ? $_POST["user_id"] : '';

    $stmt = $pdo->prepare("SELECT * FROM users WHERE user_id=?",$_SESSION["user_id"]["0"]);
    $stmt->execute([$user_id]); 
    $user = $stmt->fetch(); # get user data

}

    // query courses table to retrieve its contents            
        $cid = $_POST["cid"] ?? NULL;
        if (is_null($cid))
    {
           $stmt = $pdo->query("SELECT * FROM courses");
        }
        else
    {
           $stmt = $pdo->prepare("SELECT * FROM courses WHERE cid = ?");
           $stmt->execute([$cid]);
    }

        $results = $stmt->fetchAll(PDO::FETCH_ASSOC);

        echo '<option value="">'. "Select a course to proceed" .'</option>';

        foreach ($results as $row) {
        echo '<option value=" '. $row["cid"] .' ">'. $row["c_name"] .'</option>';                
    }

Apart from echoing $row["cid"] (course ID) and $row["c_name"] (course name) from the courses table, I also want to echo the following from the same courses table: $row["code"], $row["duration"], $row["start"]

In the users table, I have the logged in user's "user_id", "firstname", "lastname", "username", "email", which I also want to echo in the above foreach loop. That means the user must be logged in.

Thank you in advance for your time and help.