This document discusses different types of SQL injection attacks:
1. Error-based SQL injection exploits errors returned by the database directly to the user, such as debugging information.
2. Union-based SQL injection abuses the SQL UNION operator to display the results of additional queries.
3. Blind SQL injection is more difficult, as it does not return direct errors or results. The attacker must craft queries to test for conditions to extract information one bit at a time. Automated tools can help but sometimes custom scripts are needed to fully exploit blind SQL injection vulnerabilities.