Use Window Function for Running Total

SQL

Technical Specification

For each user's orders, compute a running total (cumulative sum) of total_amount ordered by created_at.

Input/Output Samples

Input:user orders

Output:Each row has running_total column

Optimal Logic Path

SELECT
  user_id,
  id AS order_id,
  total_amount,
  created_at,
  SUM(total_amount) OVER (
    PARTITION BY user_id
    ORDER BY created_at
  ) AS running_total
FROM orders;

Architectural Deep-Dive

Window functions calculate aggregates across related rows without collapsing them.