From the PHP Manual:
Warning This extension was deprecated in PHP 5.5.0, and it was removed in PHP 7.0.0. Instead, the MySQLi or PDO_MySQL extension should be used. See also MySQL: choosing an API guide. Alternatives to this function include:
mysqli_connect()
PDO::__construct()
use MySQLi or PDO
<?php
$con = mysqli_connect('localhost', 'username', 'password', 'database');