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N015-E2 Tier 2 · Core SQL · easy ecommerce · Brightlane

Return the product ID and total revenue for every product whose combined order-line revenue exceeds `$2,000`

Part of HAVING in SQL

The problem

Brightlane's merchandising team is ranking top-performing products for a promotional campaign.

Write a query to return the product ID and total revenue for every product whose combined order-line revenue exceeds $2,000.

Assumptions:

  • The order_items table contains one row per product per order.
  • Per-line revenue is quantity * unit_price; per-product revenue is the sum of that calculation across all of the product's lines.
  • The threshold (> $2,000) applies to the per-product total, not to any individual line item.

Output:

  • One row per qualifying product, with columns product_id and total_revenue.
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
  product_id,
  SUM(quantity * unit_price) AS total_revenue
FROM
  order_items
GROUP BY
  product_id
HAVING
  SUM(quantity * unit_price) > 2000

The shape

GROUP BY product_id builds per-product sums of quantity * unit_price; HAVING SUM(quantity * unit_price) > 2000 keeps only the products that clear $2,000. Product 6 lands at 11994, product 9 at 5996, down to product 30 at 2093.

Clause by clause

  • SELECT product_id, SUM(quantity * unit_price) AS total_revenue returns the grouping column with the per-product revenue alongside it. SUM walks the rows that belong to each product and adds the quantity * unit_price expression on each line.
  • FROM order_items is the source set: one row per (order, product) line.
  • GROUP BY product_id collapses those lines into one row per product. Each surviving row carries the aggregated revenue for the product.
  • HAVING SUM(quantity * unit_price) > 2000 filters those per-product rows by aggregate. The expression is repeated rather than referenced by its total_revenue alias.

Why this and not HAVING total_revenue > 2000

Referencing the alias feels natural. PostgreSQL doesn't allow it. The evaluation order is FROM → WHERE → GROUP BY → HAVING → SELECT, which means the alias total_revenue hasn't been created yet at the moment HAVING runs. The fix is to repeat the aggregate expression. It feels redundant, but the rule is fixed: anything HAVING filters on has to be expressed as an aggregate, not the name SELECT will give it.

You practiced filtering on a computed aggregate with HAVING. The same expression that built the total_revenue column has to be repeated inside HAVING — PostgreSQL doesn't allow HAVING to reference SELECT-list aliases, because the alias doesn't exist yet when HAVING runs.

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