所以我有一个2张桌子，如下所示：
项目
+-----------------+-------------+
| id | Name | Category |
+-----------------+-------------+
| 1 | Something1 | A |
| 2 | Something2 | B |
| 3 | Something3 | B |
| 4 | Something4 | A |
| 5 | Something5 | A |
+-----------------+-------------+
购买
+-----------------+-------------+
| id | Name | Number |
+-----------------+-------------+
| 1 | Something1 | 14 |
| 1 | Something2 | 10 |
| 2 | Something1 | 14 |
| 2 | Something5 | 11 |
| 2 | Something3 | 12 |
| 3 | Something4 | 18 |
| 4 | Something3 | 11 |
+-----------------+-------------+
购买表没有主键，因为带有另一个账单表的id伪造密钥包含id和类型（卖/买/借）。账单可以包含许多项目。我可以一个人加入他们
+-----------------+-------------+
|STT | name | Total |
+-----------------+-------------+
| 1 | Something1 | 28 |
| 2 | Something4 | 18 |
| 3 | Something5 | 11 |
+-----------------+-------------+
我想要什么：
+-----------------+-------------+
|STT | name | Total |
+-----------------+-------------+
| Category: A |
|-------------------------------|
| 1 | Something1 | 28 |
| 2 | Something4 | 18 |
| 3 | Something5 | 11 |
| Category: B |
|-------------------------------|
| 1 | Something3 | 23 |
| 2 | Something2 | 10 |
+-----------------+-------------+
仅使用sql可以吗？（不使用临时表）