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SQL Beginner Challenge 16: Single-Character Matching with _ (Underscore Wildcard)

Difficulty: Beginner
Estimated time: 10–15 minutes
SQL concepts: LIKE, _ (single-character wildcard), pattern precision
Goal: Match text patterns where exact character positions matter.

The Scenario

A product manager asks:

“Can we find product codes that follow a specific pattern—where one character varies, but the rest is fixed?”

You already know % matches any number of characters.
Now you’ll use _ to match exactly one character.

Database Table

`products`

column_name	type	description
product_id	INTEGER	Unique product ID
name	TEXT	Product name
sku	TEXT	Product SKU
price	DECIMAL	Product price

Sample Data

product_id	name	sku	price
201	USB-C Hub	USB1-A	34.50
202	USB-C Hub Pro	USB2-A	49.99
203	USB Flash Drive	USB10-A	19.99
204	Wireless Mouse	MOU1-B	24.99
205	Mechanical Keyboard	KEY1-B	89.00

Your Task

Write a SQL query that returns:

name
sku

…but only for products whose sku matches this pattern:

USB_-A

👉 This means:

Starts with USB
Followed by exactly one character
Then -A

Expected Output

name	sku
USB-C Hub	USB1-A
USB-C Hub Pro	USB2-A

Constraints

Use the LIKE operator
Use the _ wildcard
Do not use % for this challenge
Do not use SELECT *

Hint (Optional)

_ matches exactly one character
% matches any number of characters

Examples:

USB_-A ✅ matches USB1-A
USB_-A ❌ does not match USB10-A

SELECT name, sku FROM products WHERE sku LIKE 'USB_-A';

Explanation

LIKE 'USB_-A' matches SKUs where:
- USB is fixed
- _ represents exactly one character
- -A is fixed
This gives you precise control over pattern length.

Common Mistakes

Using % instead of _
- % would match USB10-A, which we don’t want.
Expecting _ to match multiple characters
Forgetting that _ matches exactly one character

Optional Extension (Mini Bonus)

Try:

Match MOU_-B SKUs
Combine _ and % in one pattern
Find SKUs that start with USB, have one digit, and end with -A

Next Challenge

Beginner Challenge #17: Combining Conditions with AND and OR

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

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