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N002-M4 Tier 1 · Foundations · medium ecommerce · Brightlane

Return every product category's ID and name

Part of FROM and Table References in SQL

The problem

Brightlane's front-end team is rebuilding the site navigation and needs to populate a category dropdown from the database.

Write a query to return every product category's ID and name.

Assumptions:

  • The categories table contains every product category in Brightlane's catalog.
  • Each category has an id and a name.

Output:

  • One row per category, with columns id and name.
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
  id,
  name
FROM
  categories

The shape

FROM categories reads the catalog's category list, and the two columns in the SELECT list produce exactly the value-and-label pair a UI dropdown needs to render.

Clause by clause

  • SELECT id, name returns two columns per row: the identifier the dropdown sends back when a user picks an option, and the display name the user sees. That's the standard shape for any UI-driven control — an internal ID that the rest of the system uses, paired with a human-readable label.
  • FROM categories reads every category the catalog defines. With no WHERE clause, the dropdown gets the full list — which is what the front-end needs, because hiding a category from the dropdown would silently break navigation to that part of the site.

Why this and not SELECT *

The dropdown only needs two columns. If the categories table carries more — a slug, a sort order, a parent reference — none of those go to the front-end; they'd just inflate the payload over the network without serving the UI. Returning the minimum the consumer needs is the right default any time a query feeds another system. The receiving code is built against a specific column contract, and tight column lists are how that contract stays explicit. A SELECT * query couples the front-end to whatever shape the table happens to have today, which makes both sides harder to change later.

You practiced returning a small two-column slice of a table — exactly what a UI dropdown or label-value pair needs. Picking the minimum columns the consumer needs is good query hygiene whenever a query feeds another system.

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