: This is an intentional "invalid" input (like a negative ID) designed to break the original SQL query's logic and ensure the database returns no results for the first part of the operation.
: Determining the column count is the first step toward extracting sensitive data, such as usernames and passwords. -3216' UNION ALL SELECT 34,34,34,34#
: If the page displays the number "34" several times, it confirms the site is vulnerable to SQL injection. : This is an intentional "invalid" input (like