SQL injection is a type of attack that can be used to exploit vulnerabilities in PHP applications. It occurs when malicious code is injected into a SQL query, which can then be used to gain unauthorized access to the database.

There are a number of ways to prevent SQL injection in PHP. Here are some of the best practices:

• Use prepared statements: Prepared statements are a secure way to pass user input to a database. When you use prepared statements, the user input is not embedded in the SQL query itself. Instead, the user input is passed to the database as a parameter. This prevents attackers from injecting malicious code into the SQL query.
• Use parameterized queries: Parameterized queries are similar to prepared statements, but they are not as secure. Parameterized queries use a placeholder for the user input, but the placeholder is not escaped. This means that attackers can still inject malicious code into the SQL query, but it is more difficult.
• Escape user input: Even if you use prepared statements or parameterized queries, you should still escape user input. This will prevent attackers from injecting malicious code into the string.
• Use a web application firewall (WAF): A WAF is a security appliance that can help to protect your application from SQL injection attacks. A WAF can filter out malicious traffic and prevent attackers from injecting malicious code into your application.

By following these best practices, you can help to prevent SQL injection in your PHP applications.

Here are some additional tips to prevent SQL injection in PHP:

• Use the least privilege principle: Give database users only the permissions that they need to perform their job. This will help to prevent attackers from exploiting vulnerabilities in the database.
• Keep your software up to date: Software vendors often release security patches to fix vulnerabilities. Make sure that you install security patches as soon as they are released.
• Be aware of the latest SQL injection attacks: There are new SQL injection attacks being developed all the time. It is important to be aware of the latest attacks so that you can protect your applications from them.