<?php


    public function sales_by_product() {
        $sql =
        "SELECT  products.*,
            count(oi.order_id) AS sold
        FROM    products
        LEFT OUTER JOIN orderitems AS oi
            INNER JOIN orders
                ON oi.order_id = orders.id AND orders.completed = 1
            ON oi.product_id = products.id
        GROUP BY products.id";
        $result = $this->db->query($sql);
        return $result;
    }

?>