ERROR (SQL): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'GROUP BY order_data.product_default_id' at line 7<br><br>SELECT  SUM(quantity) AS ordered_quantity
                        FROM `order`
                        LEFT JOIN order_data USING(order_id)
                        WHERE (order_state_id=1 OR order_state_id=2) AND sell_id=0
                        AND order_data.product_default_id = 
                        
                        GROUP BY order_data.product_default_id