Blind SQL Injection
Understanding SQLi Payloads: https://www.db-fiddle.com/f/nLpyQDMd49iRygnY9H7CB8/5
Guided Lab: https://portswigger.net/web-security/sql-injection/blind/lab-conditional-responses
Challenge Lab: https://portswigger.net/web-security/sql-injection/blind/lab-time-delays