Oxford, Cambridge and RSA (OCR) GCSE Computer Science Practice Exam

The symbol used with the LIKE operator in SQL to represent any combination of letters and numbers is the percent sign (%). This wildcard character can match zero or more characters, which makes it very versatile when it comes to searching for patterns in strings.

For example, if you used the SQL query `SELECT * FROM users WHERE username LIKE 'a%'`, it would return all usernames starting with the letter 'a', followed by any combination of other letters or numbers. The percent sign effectively tells the database that it should include any characters that come after 'a', making it a powerful tool for pattern matching.

The other symbols mentioned do not serve this purpose in SQL. The question reflects the understanding of pattern matching within SQL databases, where the percent sign plays a crucial role in constructing flexible queries.