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N011-M3 Tier 1 · Foundations · medium

Return the total order cost in a single column named `total_order_cost`

Part of Arithmetic and Comparison Expressions in SQL

The problem

A Brightlane operations manager is verifying the total cost of a bulk order before issuing a purchase order. The order covers 6 bundles. Each bundle is priced at $12 for the item itself plus a $3 per-bundle handling fee.

Write a query to return the total order cost in a single column named total_order_cost.

Output:

  • A single row with one column, total_order_cost, containing the full bundled total.
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Solution query
SELECT
  (12 + 3) * 6 AS total_order_cost

The shape

The parentheses bundle the per-bundle item cost and the handling fee into a single per-bundle figure, then the multiplication scales that combined cost across six bundles.

Clause by clause

  • SELECT (12 + 3) * 6 runs the parenthesised addition first: 12 + 3 returns 15, the all-in per-bundle cost. The multiplication then scales that across the order quantity and returns 90. All three operands are integers, so the result is the integer 90 — the total in whole dollars, which matches the purchase-order format the operations manager is filling in.
  • AS total_order_cost labels the column as the figure the PO is being issued for. The result reads as a procurement line item rather than a math expression.

Why this and not 12 + 3 * 6

Strip the parentheses and operator precedence reorders the calculation. 3 * 6 resolves first to 18, then 12 + 18 returns 30. That would be the answer to a different question — "one bundle's item cost plus the handling fee applied across six bundles" — and it's wrong for this prompt. Every bundle carries both costs, so both have to scale.

The parentheses are how the prompt's business logic — "each bundle is priced at $12 plus a $3 handling fee" — gets translated into the SQL evaluation order. The shape (component_a + component_b) * quantity recurs any time a per-unit cost is itself a sum: per-seat licence plus support fee, per-shipment freight plus insurance. The grouping has to be explicit, or the multiplication will only catch one of the components.

You practiced grouping a sum inside parentheses before scaling it. The recurring shape: any time a per-unit cost has multiple components and you need to multiply the bundled cost by the unit count, parentheses force the addition to complete first.

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