The string you've provided, "-1697 UNION ALL SELECT 34#" , is a classic example of a payload. This specific syntax is often used by security researchers or attackers to test if a database-driven website is vulnerable to unauthorized data access. What this string does:
: In MySQL, this character marks the rest of the query as a comment, effectively "breaking" any remaining original code that might cause the attack to fail. Why are you seeing this?
: This is the most effective defense.
To prevent these types of attacks, developers should never insert user input directly into SQL queries. Instead, you should use: