How can we calculate total customer spending?
SUM() over joined transaction records aggregates monetary totals grouped by customer.
Customer lifetime spend, revenue contribution by account, billing rollups.
SELECT c.customer_name, SUM(o.amount) AS total_spent
FROM customers c
JOIN orders o
ON c.customer_id = o.customer_id
GROUP BY c.customer_name;Practice typing production-grade SQL code for JOIN with SUM.