Не выбирает базу

<?php 
include("connections/connection.php");
session_start();
//--------------------------------------------------//
if($connection){
if (isset($_POST['username']) && isset($_POST['password']))
{
    $login = mysql_real_escape_string($_POST['username']);
    $password = md5($_POST['password']);
 
   $query = "SELECT `id`
            FROM `users`
            WHERE `username`='{$login}' AND `password`='{$password}'
            LIMIT 1";
            
    $sql = mysql_query($query) or die(mysql_error());
 
    if (mysql_num_rows($sql) == 1) {
        $row = mysql_fetch_assoc($sql);
        $_SESSION['user_id'] = $row['id'];
        $_SESSION['user_ip'] = $_SERVER["REMOTE_ADDR"]; 
        echo "ok";
        //header("Location: panel.php");
    }
    else {
        echo "no";
        //SetCookie("Login"," ");
        //header("Location: index.php");
    }
}
}
    else {
        echo('No MySQL.');
    }
 
?>

<?php
//-----------MySQL
$server="localhost";
$user="root";
$password="159753";
$db="Site";
//-----------MySQL_END
?>

<?php
include_once("../conf/db_config.php");
 
$connection=mysql_connect($server, $user, $password);
mysql_select_db($db);
?>

mysql_select_db($db,$connection);

$connection=mysql_connect($server, $user, $password);
if (!$connection) {echo 'Can\'t connect. '.mysql_error();}
$selected_db = mysql_select_db($db);
if (!$selected_db) {echo 'Can\'t select db. '.mysql_error();}

include_once("../conf/db_config.php");

include_once '../conf/db_config.php';

$db="Site";