/**

Given the following table

customer                              product
+---------------+---------+           +---------------+---------+
| id            | int     |-----+  +--| id            | int     |
| age           | int     |     |  |  | price         | double  |
| gender        | char    |     |  |  +---------------+---------+
+---------------+---------+     |  |
                                |  |  sale
                                |  |  +---------------+---------+
                                |  |  | id            | int     |
                                |  +->| product_id    | int     |
                                +---->| customer_id   | int     |
                                      +---------------+---------+
*/



/**
 * 1. Get the total revenue for all males in the customer database.
 *
 *
*/

# select * from customer limit 10;


select sum(p.price)
from customers c left outer join sales s
on c.id = s.customer_id
left outer join products p
on s.product_id = p.id
where c.gender = 'm';