MySQL总和来自两个连接表和多行

Question

I am having a problem with the following query:

SELECT sum(((ordered_items.price + ordered_items.vat) * ordered_items.qty) + orders.postage_price + orders.postage_vat) as total_price
FROM orders
JOIN ordered_items
ON orders.id_orders = ordered_items.order_id
GROUP BY orders.id_orders

The idea is to bring back the total price of an order including the postage.

• ordered_items - includes all the items ordered (so there can be multiple rows)
• orders - includes the postage price of the order (there will only ever be one row per order here)

The problem I'm having is that if an order contains multiple items in 'ordered_items' the above sum counts the postage in 'orders' multiple times.

How can I rewrite this query so the postage is only counted once?

Many thanks in advance for any help.

Answer 1

You don't need a subquery, you just need to move the postage_price and vat out of the aggregate and GROUP BY them:

SELECT sum((ordered_items.price + ordered_items.vat) * ordered_items.qty) + orders.postage_price + orders.postage_vat as total_price
FROM orders
JOIN ordered_items
ON orders.id_orders = ordered_items.order_id
GROUP BY orders.postage_price, orders.postage_vat 

Answer 2

您需要添加分组

GROUP BY ordered_items.order_id

Answer 3

SELECT items.total + orders.postage_price + orders.postage_vat) AS total_price
FROM orders
JOIN (SELECT order_id, SUM((ordered_items.price + ordered_items.vat) * ordered_items.qty) AS total
    FROM ordered_items
    GROUP BY order_id) items
ON orders.id_orders = items.order_id