title: How to pass database connection instance between PHP files without redeclaring it
body: <p>I have created a database connection instance in PHP like: </p>
  
  <pre><code>$mysqli = mysqli_connect("localhost", "root", "blabla", "blabla");
  </code></pre>
  
  <p>I need to pass this database connection to other PHP files, since I have an HTML form that first inserts data into a database and then it goes to a PHP page that retrieves data. </p>
  
  <p>I know that I must not instantiate the database connection each time but I do not know how to do it, because I am not so familiar with OO PHP. </p>