给定组类型的Mysql从其他表中获取计数和总和

Question

我有两张桌子。用户和transactions.lets说类型1是学生，类型2是教师

用户：

+----+--------+--------------+
| id | name   | user_type_id |
+----+--------+--------------+
|  1 | Noob   |            1 |
|  2 | Coder  |            2 |
+----+--------+--------------+

交易方式：

+----+---------+--------+
| id | user_id | amount |
+----+---------+--------+
|  1 |       1 |     10 |
|  2 |       2 |     10 |
|  3 |       1 |     10 |
+----+---------+--------+

我想获得每个user_type_id的总和和计数;像这样的东西

user_type_id:1 
sum_of_transaction: 20,
number_of_transactions: 2,

user_type_id:2
sum_of_transaction: 10,
number_of_transactions: 1

我怎样才能做到这一点？ Noob在这里

Answer 1

select aa.user_type_id, sum(bb.amount) as sum_of_transaction,
       count(bb.id) as number_of_transactions 
from users aa inner join transactions bb on aa.id = bb.user_id 
group by aa.user_type_id

Answer 2

对于sum_of_transaction：select sum(amount) as sum_of_transaction from transactions where user_id = ?;

对于number_of_transactions：select count(amount) as number_of_transactions from transactions where user_id = ?;