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N014-H2 Tier 2 · Core SQL · hard ecommerce · Brightlane

Return each customer's ID alongside their total spend across non-cancelled orders

Part of GROUP BY in SQL

The problem

Brightlane's retention team wants each customer's total spend on orders that actually went through — excluding any cancelled orders.

Write a query to return each customer's ID alongside their total spend across non-cancelled orders.

Assumptions:

  • The orders table contains every order Brightlane has processed.
  • An order is cancelled if status = 'cancelled'; every other status counts toward the customer's spend.
  • Cancelled orders do not contribute to any customer's per-customer total.

Output:

  • One row per customer with at least one non-cancelled order, with columns customer_id and total_spend.
Schema · ecommerce 5 tables
categories
id integer
name text
parent_id? integer
products
id integer
name text
category_id integer
price numeric
stock_qty integer
attributes? jsonb
order_items
id integer
order_id integer
product_id integer
quantity integer
unit_price numeric
customers
id integer
name text
email text
city? text
country text
created_at timestamptz
is_active boolean
orders
id integer
customer_id integer
ordered_at timestamptz
status text
total_amount numeric
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Solution query
SELECT
  customer_id,
  SUM(total_amount) AS total_spend
FROM
  orders
WHERE
  status <> 'cancelled'
GROUP BY
  customer_id

The shape

WHERE status <> 'cancelled' removes cancelled orders from the row set before any grouping happens. GROUP BY customer_id then partitions the survivors by buyer, and SUM(total_amount) adds up only the non-cancelled order amounts inside each partition. The cancelled orders never enter the sum at all, which is the correct meaning of "total spend on orders that actually went through."

Clause by clause

  • SELECT customer_id, SUM(total_amount) AS total_spend returns the customer ID and their non-cancelled spend total. customer_id is in GROUP BY; the sum is the aggregate.
  • FROM orders is the full order history, cancelled orders included for now.
  • WHERE status <> 'cancelled' runs before grouping. Every order whose status is 'cancelled' is removed from the row set. Every other status survives, including delivered, shipped, and pending.
  • GROUP BY customer_id partitions the surviving rows by buyer. SUM(total_amount) runs once per buyer's bucket, adding up only the non-cancelled amounts.

Why this and not a per-status exclusion inside the sum

A learner might reach for SUM(total_amount) WHERE status <> 'cancelled' written inline, but that is not a valid SQL form. The filter and the aggregate are separate clauses, and they run in a fixed order: WHERE first, then GROUP BY, then aggregates. Putting the cancellation filter in WHERE is the canonical way to scope the sum to non-cancelled orders. Customer 17's non-cancelled total of 4845 reflects every delivered, shipped, and pending order they have, with cancelled amounts removed before the sum saw them.

You practiced filtering at the row level (WHERE) rather than at the group level (HAVING). 'Exclude cancelled orders' is a per-row condition, so it belongs in WHERE — not HAVING.

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