如何计算每年销售的产品总量？

Question

我有 3 张桌子：

1. 产品（有产品 ID、价格等）
2. 订单（包含订单 ID、日期等）
3. orders_products（包含产品数量等订单详情）

我想计算每年销售的产品总量。为此，我编写了以下查询：

SELECT YEAR(`o`.`date_purchased`) AS year,
       SUM(`op`.`products_quantity`) AS TotalUnits,
       `p`.`products_id`,
       `p`.`products_price` AS price,
       ( SUM(`op`.`products_quantity`) * `p`.`products_price` ) AS TotalAmount
FROM   `orders` AS `o`
       INNER JOIN `orders_products` AS `op`
               ON `o`.`orders_id` = `op`.`orders_id`
       INNER JOIN `products` AS `p`
               ON `op`.`products_id` = `p`.`products_id`
GROUP  BY `p`.`products_id`
ORDER  BY year

它给了我以下结果集：

它给了我按产品分组的总金额。但我想得到按年份分组的总金额。

所以对于 2016 年（以及其他年份），我想要以下结果：

2016     10,606 (since 6478 + 632 + 2072 + 1424)

但我无法计算按年份分组的总金额，因为每种产品的价格不同。那么如何修改我现有的查询以获取每年销售的产品总量？

如果单用 MySQL 做不到，那我会毫不犹豫地使用 PHP。

Answer 1

你只需要把数量和价格的乘积带入SUM，这样每个产品的数量就乘以它自己的价格：

SELECT YEAR(`o`.`date_purchased`) AS year,
       SUM(`op`.`products_quantity`) AS TotalUnits,
       SUM(`op`.`products_quantity` * `p`.`products_price`) AS TotalAmount
FROM   `orders` AS `o`
INNER JOIN `orders_products` AS `op` ON `o`.`orders_id` = `op`.`orders_id`
INNER JOIN `products` AS `p` ON `op`.`products_id` = `p`.`products_id`
GROUP  BY year
ORDER  BY year