N001-E1 Tier 1 · Foundations · easy

Return the gross profit per unit

Part of SELECT and Column Expressions in SQL

The problem

Brightlane's merchandising team is evaluating margin on a new product line ahead of the spring catalog launch. One item in the line sells for $149.99 and carries a production cost of $89.50 per unit.

Write a query to return the gross profit per unit.

Output:

A single row with one column, gross_profit.

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Solution query

SELECT
  149.99 - 89.50 AS gross_profit

The shape

The subtraction inside the SELECT does the work, and the AS alias makes the result readable as a business quantity instead of a math expression.

Clause by clause

SELECT 149.99 - 89.50 evaluates the subtraction once and returns 60.49. There's no FROM because there's no table to read from; the two values come straight from the prompt as literals — 149.99 for the sale price, 89.50 for the production cost. The result carries two decimal places because both inputs do; PostgreSQL infers the scale of a numeric expression from its operands.
AS gross_profit labels the output column so the result reads as a domain quantity. Without it, PostgreSQL would label the column ?column?, which is fine for a quick check but useless once the result has to feed anything downstream — a spreadsheet, a report, another query.

You practiced returning a labeled expression with AS. Naming computed columns is the foundation for every query that produces derived values.

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