How to stop SQL injection through website URL in CodeIgniter?

Please follow the steps below:

1. Access a webpage on the browser window.
2. Type any special character after the link, and press enter.
3. If the page loads as usual, then the page is not secured against SQL injection.
4. Now open the file manager in cPanel, and go to the installation folder.
5. Click open the config folder, located inside the application folder.
6. Open the config.php file.
7. Scroll down, and you can see all permitted characters.
8. Allow only the alphabets, numeric, underscore and hyphen.
9. View the web page again.
10. The page does not load this time.
11. This is the first line of defense for your website.