SolveWithSQL

Difficulty: Beginner
Estimated time: 5–10 minutes
SQL concepts: DISTINCT, unique values, de-duplication
Goal: Return unique values from a column (a common reporting requirement).

The Scenario

A product manager asks:

“Which product categories do we currently have?”

They don’t want a full product list. They want a unique list of categories—no duplicates.

Your task is to query the products table and return each category only once.

Database Table

products

column_name	type	description
product_id	INTEGER	Unique product ID
name	TEXT	Product name
category	TEXT	Product category
price	DECIMAL	Product price
stock_qty	INTEGER	Units in stock
created_at	TIMESTAMP	When the product was created

Sample Data (for context)

product_id	name	category	price
101	Wireless Mouse	Accessories	24.99
102	Mechanical Keyboard	Accessories	89.00
103	27-inch Monitor	Displays	229.99
104	USB-C Hub	Accessories	34.50
105	Laptop Stand	Workspace	39.99

Your Task

Write a SQL query that returns a unique list of:

• category

From the products table.

Expected Output

category
Accessories
Displays
Workspace

(Order is not required unless you add ORDER BY.)

Constraints

• Use DISTINCT
• Return only the category column
• Do not use GROUP BY (we’ll cover that later)

Hint (Optional)

DISTINCT removes duplicate rows from your result set based on the selected columns.

Explanation

• DISTINCT ensures duplicate category values are collapsed into a single result.
• This is often used for:
  • Dropdown lists
  • Summary reporting
  • Data validation checks

Common Mistakes

1. Using DISTINCT on the wrong columns
   SELECT DISTINCT category, name FROM products; This returns unique pairs of category + name, not unique categories.
2. Assuming DISTINCT sorts results
   • DISTINCT does not sort. If you want sorting, add ORDER BY.

Optional Extension (Mini Bonus)

1. Return unique categories sorted alphabetically.
2. Return unique categories only for Accessories-priced products above 50 (combine WHERE + DISTINCT).

Next Challenge

If you want to keep going, the next beginner step is:

Beginner Challenge #6: Group and Summarize with GROUP BY

🔗 View reference solution on GitHub
(After you’ve tried the challenge)

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