mysql - 从 2 个表中选择总数量

Question

在 MySQL 中我有 4 个表:

 - product(id)
 - order(id)
 - order_detail_1(id, product_id, order_id, qty)
 - order_detail_2(id, product_id, order_id, qty)

我想获取按产品分组的 2 个表(order_detail_1、order_detail_2)中销售的产品数量的总和

产品可以存在于 order_detail_1 中，但不能存在于 order_detail_2 中，反之亦然

我测试了这个查询并且它有效，但我想要一个没有联合和子查询的更简单的查询。

select tmp.product_id ,sum(tmp.qty)  from
(
(
select order_detail_1.product_id ,sum(order_detail_1.qty) 
from order_detail_1
    inner join order on order_detail_1.id_order = order.id
    where order_detail_1.product_id is not null
    group by order_detail_1.product_id
)
union all
(
select order_detail_2.product_id ,sum(order_detail_2.qty) 
from order_detail_2
    inner join order on order_detail_2.id_order = order.id
    where order_detail_2.product_id is not null
    group by order_detail_2.product_id
)
) tmp
group by tmp.product_id

Answer 1

看起来您没有使用 order 表，而是检查它是否存在，因此您可以使用 EXISTS()

SELECT p.product_id,sum(p.qty) as qty
FROM (SELECT product_id,qty,id_order FROM order_detail_1
      WHERE product_id IS NOT NULL
      UNION ALL 
      SELECT product_id,qty,id_order FROM order_detail_2
      WHERE product_id IS NOT NULL) p
WHERE EXISTS(SELECT 1 FROM order o 
             WHERE o.id = p.id_order)
GROUP BY p.product_id