我想問如果分別對帳號和密碼驗證,密碼錯誤,就顯示密碼錯誤,而帳號錯誤,就顯示沒有註冊,的方法?
目前我不知道要從哪裡修改,請大家幫忙，感謝！

<?php
session_start(); //啟用 session 功能
header("Content-type: text/html; charset=utf-8");
require_once "dbtools.inc.php"; 
$link = create_connection(); 
$u_email = mysqli_real_escape_string($link, $_REQUEST['user_email']);
$u_password = mysqli_real_escape_string($link, $_REQUEST['user_password']);

$sql = "SELECT * FROM `member` WHERE `u_email` = '{$u_email}' ";
$result = execute_sql($link, "member_db", $sql); 
   if(mysqli_num_rows($result)=0) {
     $row = mysqli_fetch_assoc($result);
     $_SESSION['u_email'] = $row['u_email'];

     header("Location: first.html");
  }
  else  {
    mysqli_free_result($result);
    mysqli_close($link);
    echo "<script>alert('**沒有註冊,請註冊**');window.history.back();</script>"; 

 }

mysqli_free_result($result);
mysqli_close($link);