The example of inurl:index.php?id= is just the tip of the iceberg. There are dozens of variations of this dork that can help you find other common SQL injection vectors.
a rite of passage for many beginners in the 2000s and 2010s. Internet Archeology inurl index.php%3Fid=
Below is an article explaining how this structure works and what it means for website development and security. Understanding Dynamic URLs: A Guide to index.php?id= The example of inurl:index