Get ID and name of each customer and the total sum (sum of quantity of products purchased)

Question

I'm struggling with this JOIN + SUM query

What I have are these following tables (Client, orders, product)

client_id	name
1	Frank
2	Emile
3	Rose
4	Laura
5	Samuel

order_number	client_id	product_id	units_sold
1	4	1	11
2	3	2	8
3	5	3	18
4	4	4	19
5	3	5	12

product_id	description	price
1	Rice	26.10
2	Coffee	12.50
4	Sugar	13
5	Beans	5.40
3	Milk	30.00

What I'm trying to do is generate a query that shows the ID and name of each customer and the total sum (sum of quantity of products purchased).

So far, my logic without breaking it is this:

Select 
c.client_id, c.first_name
from client c
INNER JOIN orders o on o.client_id = c.client_id

I want to add the SUM part to it but whenever I try it, the new query line doesn't work

Answer 1

If you just want the sum of quantity of products:

SELECT c.client_id, c.first_name, SUM(o.units_sold)
FROM
    client c
    INNER JOIN orders o ON o.client_id = c.client_id
GROUP BY c.client_id, c.first_name;

But if you also want to see the price:

SELECT c.client_id, c.first_name, SUM(o.units_sold), 
SUM(o.units_sold*p.price)
FROM
    client c
    INNER JOIN orders o ON o.client_id = c.client_id
    INNER JOIN products p ON o.product_id = p.product_id
GROUP BY c.client_id, c.first_name;