Question

I have a simple question but I can’t find an answer (please give me a link if that question is on stackoverflow forum).
Table has orderid and quantity columns.
How to select orderid, quantity, total_in_order, where total_in_order is a sum of quantity for current orderid
So the table looks the same, but with additional column.
Example:

orderid - quantity - **total_in_order**
 1      -  43      - **78**
 1      -  24      - **78**
 1      -  11      - **78**
 2      -  31      - **31**
 3      -   9      - **25**
 3      -  16      - **25**

So, how to modify SELECT orderid, quantity, SUM(quantity) from orders; ?
Thank you.

Answer 1

Use a join to a subselect. In the subselect calculate the totals for each orderid.

SELECT
    orders.orderid,
    orders.quantity,
    totals.total_in_order
FROM orders
JOIN
(
    SELECT orderid, SUM(quantity) AS total_in_order
    FROM orders
    GROUP BY orderid
) AS totals
ON orders.orderid = totals.orderid