SQL：根据输入派生值

Question

表格交易：business_key = customer_id

customer_id|product_type|amount
-------------------------------
cus1       | shoes      | 100
cus1       | shoes      |  50
cus1       | clothes    | 100
cus2       | clothes    | 500
cus2       |clothes     |  21

table transactionsbycustomer：business_key = customer_id + product_type

customer_id|product_type|amount
-------------------------------
cus1       |shoes       |150
cus1       |clothes     | 50
cus2       |clothes     |521

我需要通过客户＆＃39;在＆＃39; Transactions中获得金额的值。使用SQL的表？请帮忙！

Answer 1

这是非常基本的SQL。

SELECT customer_id, product_id, sum(amount) as total
FROM transactionsbycustomers
GROUP BY customer_id, product_id