N001-E2 Tier 1 · Foundations · easy

Return the total cost for a 12-month subscription

Part of SELECT and Column Expressions in SQL

The problem

Streamhub is tracking software vendor spend ahead of next quarter's budget review. A procurement analyst is documenting the cost of one analytics tool that is billed at $29.99 per month on a monthly cycle.

Write a query to return the total cost for a 12-month subscription.

Output:

A single row with one column, annual_cost.

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Solution query

SELECT
  29.99 * 12 AS annual_cost

The shape

The multiplication inside the SELECT rolls a monthly cost into an annual one, and AS annual_cost makes the result readable in the business unit the procurement analyst is working in.

Clause by clause

SELECT 29.99 * 12 evaluates the multiplication once and returns 359.88. There's no FROM because there's no table to read from; the rate and the cycle length come straight from the prompt as literals. The result carries two decimal places because 29.99 does — when PostgreSQL multiplies a numeric by an integer, it keeps the scale of the more precise operand. So the dollars-and-cents precision survives the calculation intact.
AS annual_cost labels the output column so the result reads as a domain quantity. Without it, the column would land as ?column? in the budget review — readable to the analyst running the query, useless to anyone else looking at the screenshot later. Labelling at the source is what makes a one-off calculation portable into a report or a spreadsheet without renaming it after the fact.

You practiced multiplying inside a SELECT and labeling the result with AS. The same shape recurs anytime a computed value needs a clear name in the result.

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