合并列中的重复值

Question

我有一个表cart_items，其中包含以下数据

+-----+---------+---------+------------+----------+
| id  | user_id | cart_id | product_id | quantity |
+-----+---------+---------+------------+----------+
| 303 |       9 |      44 |          1 |        2 |
| 305 |       9 |      44 |          3 |        1 |
| 307 |       9 |      44 |          3 |        1 |
| 308 |       9 |      44 |          2 |        1 |
| 309 |       9 |      44 |          6 |        1 |
| 310 |       9 |      44 |          2 |        1 |
+-----+---------+---------+------------+----------+

我的问题是有重复的产品。我想要的桌子是这个

+-----+---------+---------+------------+----------+
| id  | user_id | cart_id | product_id | quantity |
+-----+---------+---------+------------+----------+
| 303 |       9 |      44 |          1 |        2 |
| 305 |       9 |      44 |          3 |        2 |
| 308 |       9 |      44 |          2 |        2 |
| 309 |       9 |      44 |          6 |        1 |
+-----+---------+---------+------------+----------+

所以区别在于重复的product_id被合并并增加了quantity。

有没有一种简单的方法可以通过SQL查询做到这一点？

Answer 1

您需要group by user_id, cart_id, product_id并进行汇总：

select
  min(id) id, user_id, cart_id, product_id, sum(quantity) quantity
from cart_items
group by user_id, cart_id, product_id