表:项目
+---+-----------+
|id | name |
+---+-----------+
| 1 | Product-A |
| 2 | Product-B |
+---+-----------+
表:订单
+---+-----+------------+
|id |price| orderer_id |
+---+-----+------------+
| 1 | 100 | 53 |
| 2 | 240 | 54 |
| 3 | 200 | 54 |
| 4 | 150 | 53 |
+---+-----+------------+
表:item_order
+----+--------+---------+----------+
| id |order_id| item_id | quantity |
+----+--------+---------+----------+
| 1 | 1 | 1 | 2 |
| 2 | 1 | 2 | 3 |
| 3 | 2 | 2 | 2 |
| 4 | 3 | 1 | 1 |
| 5 | 3 | 2 | 1 |
| 6 | 4 | 1 | 2 |
| 7 | 4 | 2 | 2 |
+----+--------+---------+----------+
提取什么:
对于每个orderer_id,number_of_order,total_quantity,total_price
+---------+-----------------+----------------+-------------+
| orderer | number_of_order | total_quantity | total_price |
+---------+-----------------+----------------+-------------+
| 53 | 2 | 9 | 250 |
| 54 | 2 | 4 | 440 |
+---------+-----------------+----------------+-------------+
目前的做法:
使用相关子查询
select orderer_id as orderer,
count(*) as number_of_order,
sum(select quantity from item_order where item_order.order_id = orders.id) as total_quantity,
sum(price) as total_price
from orders
order by orderer_id
可以通过将item_order与订单连接来解决吗?如果有,怎么样?
我想的另一种方法 –
>从订单中选择…
>从item_order中选择…
>根据应用层的要求进行组合和格式化
您可以假设,订单和item_order表会变得更大,哪种解决方案会更好?
最佳答案 由于从order到item_order的一对多关系,在子查询中执行聚合和在派生表中JOIN更容易:
SELECT o.orderer_id,
COUNT(o.id) AS number_of_order,
SUM(io.quantity) AS total_quantity,
SUM(o.price) AS total_price
FROM orders o
JOIN (SELECT order_id, SUM(quantity) AS quantity
FROM item_order
GROUP BY order_id) io ON io.order_id = o.id
GROUP BY o.orderer_id
输出:
orderer_id number_of_order total_quantity total_price
53 2 9 250
54 2 4 440
我希望这比相关子查询更快,因为必须对orders表中的每一行执行查询,而派生表的查询虽然更复杂,但只执行一次.我还希望这比在应用程序层执行两个查询和组合的选项更快.