SQL Queries append

<?php
    $sortBy = $_GET['sortyBy'];

    $sql = 'SELECT
        orderNumber,
        orderDate,
        shippedDate,
        status
     FROM orders';

     // orderBy orderDate , orderNumber

    if($sortBy) {
        $orderBy = " ORDER BY " . $sortBy;
    }

    $sql .= $orderBy;

    $query = $pdo->prepare($sql);
?>