555-1)) OR 558=(SELECT 558 FROM PG_SLEEP(0))--

That string looks like a time-based SQL injection payload for PostgreSQL (it references pg_sleep). I won’t assist with exploiting systems, but I can help you understand the concept and how to defend against it for exam prep.

What this type of payload is illustrating (high level):

• Time-based blind SQL injection: the attacker injects SQL that makes the database wait (sleep) if a condition is true, allowing inference about data even when there’s no visible error message.
• The idea behind something like that is to alter the query logic (e.g., OR something) and induce a delay, then measure response time to deduce information about the database.

Defensive/examination-focused topics you should know:

• How to prevent SQL injection
  • Use parameterized queries / prepared statements in your language of choice (e.g., psycopg2, JDBC, etc.).
  • Avoid string concatenation or manual escaping of user input in SQL.
  • Validate and sanitize inputs (type checks, length checks, allowlists).
  • Use an ORM with proper parameter binding, and understand its security guarantees.
  • Apply least privilege: the DB user used by the app should have only the necessary permissions (no superuser rights).
  • Minimize the exposure of dangerous functions (e.g., consider restrictions on functions like pg_sleep where possible).
  • Implement input handling and output encoding consistently across the stack.
• Types of SQL injection (for exams)
  • Boolean-based (true/false) injections
  • Union-based injections
  • Error-based injections
  • Time-based (like pg_sleep) injections
• How to test safely (in a lab, not on systems you don’t own)
  • Use intentionally vulnerable environments like DVWA, WebGoat, or OWASP WebGoat in a sandbox.
  • Practice identifying when user input reaches SQL queries and how parameterization eliminates the risk.
• Safe coding examples
  • Provide concrete examples of vulnerable vs. secure code in your language (e.g., Python with and without parameterized queries, or Java with PreparedStatement).

If you’d like, tell me your exam focus (language you’re using, or a particular topic), and I can give you safe, defensive example code and a checklist to study. And remember: never test injections on systems you don’t have explicit permission to assess.