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.