How sql injection works?

SQL injection is a website hacking technique where attackers first find the vulnerability in web site then attack on that website through SQL injection.

Generally SQL injection is used for injecting some malicious SQL query in database of the website to find information from the database.

As shown in below table the user provide his/her username and password at the same time the attacker send some malicious code in web server and instead of user the attacker gets logins into the server .