Introduction to SQL Injection

SQL Injection is a code injection technique that attackers use to insert malicious SQL code into a web application’s database query. The attacker can exploit this vulnerability to manipulate the application’s database, often with devastating effects. In this tutorial, we’ll cover the basics of SQL Injection, its types, and how to prevent it.

Understanding SQL Injection

SQL Injection attacks occur when an attacker is able to insert a series of SQL queries into a ‘query string’ and trick the application into executing them. This can lead to unauthorized access to sensitive data, data loss, or even data corruption. To understand SQL Injection better, let’s look at a simple example:

// Unsafe SQL query
String query = "SELECT * FROM users WHERE username = '" + username + "' AND password = '" + password + "'";

In the above example, if an attacker inputs ' OR '1'='1 as the username and password, the query becomes:

SELECT * FROM users WHERE username = '' OR '1'='1' AND password = '' OR '1'='1'

This will return all the users, allowing the attacker to bypass the login.

Types of SQL Injection

There are mainly three types of SQL Injection:

  • In-band SQLi
  • Blind SQLi
  • Out-of-band SQLi

Each type has its own characteristics and methods of exploitation. For more details, you can check out this article by OWASP.

Preventing SQL Injection

Preventing SQL Injection involves securing your database from malicious queries. Here are some methods:

  • Use Prepared Statements (Parameterized Queries)
  • Use Stored Procedures
  • White List Input Validation
  • Least Privilege Principle

By implementing these methods, you can significantly reduce the risk of SQL Injection attacks. For a more detailed guide on preventing SQL Injection, check out this cheat sheet by OWASP.


Understanding SQL Injection and its prevention methods is crucial for securing your web applications. Always remember, the best defense is a good offense. Stay safe!