Question

I have a table with purchased orders data.
Each row contails the amount of certain item purchased, cost per item and the order number group. Each different item purchased is a new row with same order number.

I basically want to return the total cost for that order. I have tried the following but am getting nowhere:

SELECT order_number, SUM( sub_total ) AS `total`
FROM
  SELECT order_number, SUM( SUM( amount ) * SUM( cost_per_item ) ) AS `sub_total`
    FROM `ecom_orders`
   WHERE member_id = '4'
GROUP BY order_number
ORDER BY purchase_date DESC 

Answer 1

Pretty much any SQL-92 compliant RDBMS will take this:

SELECT
order_number
,SUM(amount * cost_per_item) AS total
,purchase_date
FROM
ecom_orders
WHERE member_id = '4'
GROUP BY order_number,purchase_date
ORDER BY purchase_date DESC