This is the gold standard. Instead of building a query string with user input, you use placeholders ( ? ). The database treats the input strictly as data, never as executable code.
It uses functions like CONCAT and GROUP BY to intentionally trigger a duplicate-key error. The database's error message will then "leak" the information hidden inside the query (in this case, the results of the SELECT 1 or version info) back to the attacker's screen. This is the gold standard
These are hexadecimal representations of characters (like 'qbqvq') used as delimiters so the attacker can easily spot their "stolen" data in the middle of a messy error message. Why is it dangerous? The database treats the input strictly as data,
Ensure your database user account only has the permissions it absolutely needs. For example, a "read-only" web user shouldn't be allowed to access INFORMATION_SCHEMA . you use placeholders ( ? ).