CTE used in a JOIN

Question

CTE used in a JOIN

Accepted Answer

The CTE aggregates orders per customer: customer_id 1 (Alice) = 300, customer_id 2 (Bob) = 50. The outer query joins customers to the CTE result by id. Both customers match, so both appear in the output. Using a CTE here avoids embedding the GROUP BY logic directly inside the JOIN, keeping the query easier to read.