mysqli connection example

<?php

define("DB_HOST", "mysql.dungla.com");
define("DB_USER", "dungla");
define("DB_PASS", "password");
define("DB_NAME", "2017_mukeshdak");

$connection = mysqli_connect(DB_HOST, DB_USER, DB_PASS, DB_NAME);

if(!$connection) die("Mysqli connection failed " . mysqli_error($connection));

if( ($_SERVER['REQUEST_METHOD'] == 'POST') && isset($_POST['username']))
{
    $username = mysqli_real_escape_string($connection, $_POST['username']);
    $password = mysqli_real_escape_string($connection, $_POST['password']);
    // Lines above ensures, protection against SQL injection.

    $query = "SELECT * from users where username LIKE '".$username."' ";

    $result = mysqli_query($query);

    if($result)
    {
        while($row = mysqli_fetch_assoc($result)
        {
            echo $row['username'];
        }

    }
}