There are a few solutions to your problem.
The way with MySQLi would be like this:
<?php
$connection = mysqli_connect('localhost', 'username', 'password', 'database');
To run database queries is also simple and nearly identical with the old way:
<?php
// Old way
mysql_query('CREATE TEMPORARY TABLE `table`', $connection);
// New way
mysqli_query($connection, 'CREATE TEMPORARY TABLE `table`');
Turn off all deprecated warnings including them from mysql_*:
<?php error_reporting(E_ALL ^ E_DEPRECATED);
The Exact file and line location which needs to be replaced is “/System/Startup.php > line: 2 ” error_reporting(E_All); replace with error_reporting(E_ALL ^ E_DEPRECATED);