Reports: joins with grouping

The real power comes from combining what you have learned: join two tables, group the joined rows, and summarise each group with an aggregate.

A common report is "how much has each customer spent?" — join customers to their orders, group by customer, and SUM the totals.

One row per customer

SELECT customer.name,
       COUNT(*) AS orders,
       ROUND(SUM(orders.total), 2) AS spent
FROM customer
INNER JOIN orders ON customer.id = orders.customer_id
GROUP BY customer.id
ORDER BY customer.name;

Reading it in order: join the tables, group the rows by customer, then for each group count the orders and add up the totals.