新手求问，为什么select不了

查询返回false，但是语句在数据库里是能实现的，求大神帮忙找找错
/**

  • Created by PhpStorm.
  • User: Administrator
  • Date: 2016/11/25
  • Time: 14:46 */

header("Content-type:text/html;charset=utf-8");
include "db_users.php";
if ($_SERVER['REQUEST_METHOD']=="POST")
{
$account = $_POST['account'];
$psw = $_POST['psw'];
print_r($account);
echo "
";
print_r($psw);
echo "
";
$result= mysqli_query($con,"SELECT * FROM shop_users WHERE email = '$account' OR phone_num = $account OR username = ' $account' ");
var_dump($result);
$num = mysqli_num_rows($result);
var_dump($num);

db_users.php的代码
$con=mysqli_connect('localhost') or die("数据库连接失败".mysqli_error($con));
mysqli_query($con,"set names utf8");
mysqli_select_db($con,'shop_users');
图片说明

sql语句拼接不能这么写，否则这些变量都会被当作普通文字。
http://www.cnblogs.com/shanmao/archive/2013/07/29/3223309.html

"SELECT * FROM shop_users WHERE email = ”'”+$account+“' ”OR phone_num = ”'”+$account+“' ” OR username = ”'”+$account+“' ”);