[SOLVED] How to make a sum selection of tuples with relational algebre

Question

I have a table of customers and I want to know the total amount each client spent . I can make a sum for all the column amount, or just for one customer with the clause "where id_customer=x" but how to make the sum for each customer?

Answer 1

use SUM and GROUP BY together

SELECT customer_id, SUM(order_amount)
FROM orders
GROUP BY customer_id;

this might help:

https://www.w3resource.com/sql/aggregate-functions/sum-with-group-by.php

Answer 2

great :)
marked as solved for anyone else who encounter this problem (and search for it <.<)

Answer 3

thank you guys, Burey have the solution.