檢查數據庫中是否已經存在用戶名和電子郵件

Question

我剛開始使用php，並且嘗試創建系統以拒絕“創建帳戶”（如果您鍵入現有的用戶名或密碼）。謝謝，對不起我的英語不好。 我已經嘗試過了。不起作用： 鏈接

這是我的PHP：

<?php
session_start();

$db = mysqli_connect("localhost", "root", "", "itsnikola");

if (isset($_POST['register_btn'])) {
    $name = mysqli_real_escape_string($db, $_POST['name']);
    $lastname = mysqli_real_escape_string($db, $_POST['lastname']);
    $username = mysqli_real_escape_string($db, $_POST['username']);
    $email=mysqli_real_escape_string($db, $_POST['email']);
    $password=mysqli_real_escape_string($db, $_POST['password']);
    $password2=mysqli_real_escape_string($db, $_POST['password2']);

    if ($password == $password2) {
        session_start();
        $password = ($password);
        $sql="select * from account_info where (username='$username' or email='$email')";

        if (mysqli_num_rows($res) > 0) {
          $row = mysqli_fetch_assoc($res);
          if ($username==$row['username'])
          {
              $_SESSION['message'] = "Username je vec registrovan";
          }
          else($email==$row['email']){
              $_SESSION['message'] = "Email je vec registrovan"
          }
       else
        {
        $sql = "INSERT INTO users(name, lastname, username, email, password) VALUES('$name' , '$lastname' , '$username' , '$email' , '$password')";
        mysqli_query($db, $sql);
        $_SESSION['message'] = "Sada si ulogovan";
        $_SESSION['message'] = $username;
        header("location:login.php");
    }else {
        $_SESSION['message'] = "Ne podudaraju se lozinke!";
    }
}
?>

Answer 1

if (mysqli_num_rows($res) > 0)您將在此行之前錯過非常重要的行

$sql="select * from account_info where username='$username' or email='$email' ";

$res = mysqli_query($db, $sql); // you're missing this line to query by $sql 

if (mysqli_num_rows($res) > 0) {
// you're other code goes here 
}

Answer 2

首先， session_start()被調用兩次。
if ($password == $password2) {
您的代碼也缺少; 和一些} （用於正確關閉if條件）

現在的解決方案：
在處理數據庫查詢的結果之前，需要連接到數據庫並執行適當的SQL命令，然后您才能獲得所需的結果。 您的代碼缺少此過程。
在下面的代碼中檢查我的評論↓，然后在更正的代碼中再次檢查

if ($password == $password2) {
        session_start(); // remove this repeated call
        $password = ($password);
        $sql="select * from account_info where (username='$username' or email='$email')";
        if (mysqli_num_rows($res) > 0) { // $res isn't defined
          $row = mysqli_fetch_assoc($res);
          if ($username==$row['username'])
          {
              $_SESSION['message'] = "Username je vec registrovan";
          }
          else($email==$row['email']){  // `else` doesn't work this way, use `elseif`
              $_SESSION['message'] = "Email je vec registrovan"  // ; missing
          }

更正的代碼 ：

if (isset($_POST['register_btn'])) {
    $name      = mysqli_real_escape_string($db, $_POST['name']);
    $lastname  = mysqli_real_escape_string($db, $_POST['lastname']);
    $username  = mysqli_real_escape_string($db, $_POST['username']);
    $email     = mysqli_real_escape_string($db, $_POST['email']);
    $password  = mysqli_real_escape_string($db, $_POST['password']);
    $password2 = mysqli_real_escape_string($db, $_POST['password2']);

    if ($password == $password2) {
        $password = ($password);
        $sql      = "SELECT * FROM users WHERE (username='$username' OR email='$email')";
        $res      = mysqli_query($db, $sql); // you were calling $res but it wasn't defined; this connects to the DB and executes SQL and then assigns the result
        if (mysqli_num_rows($res) > 0) {
            $row = mysqli_fetch_assoc($res);
            if ($username == $row['username']) {
                $_SESSION['message'] = "Username je vec registrovan";
            } elseif ($email == $row['email']) {  // changed `else` to `elseif` to include the condition, `else` doesn't accept conditional checks
                $_SESSION['message'] = "Email je vec registrovan";  // added ;
            }
        } else {
            $sql = "INSERT INTO users (name, lastname, username, email, password) VALUES ('$name', '$lastname', '$username', '$email', '$password')";
            if (mysqli_query($db, $sql)) {
                // New record inserted
                $_SESSION['message'] = "Sada si ulogovan";
                $_SESSION['message'] = $username;
                header("location: login.php");
            } else {
                echo("Error: " . mysqli_error($db));
            }
        }
    } // required to close the password checking condition
    else {
        $_SESSION['message'] = "Ne podudaraju se lozinke!";
    }
}

建議：

1. 使用准備好的語句，而不是直接將用戶提供的輸入傳遞給SQL
   （至關重要的是，您當前的代碼容易受到SQL注入的攻擊）
2. 使用支持PHP並提供語法高亮顯示的IDE（Atom，Visual Studio Code，PhpStorm等）

Answer 3

我已經試過了

<?php
session_start();

$db = mysqli_connect("localhost", "root", "", "itsnikola");
if (isset($_POST['register_btn'])) {
    $name      = mysqli_real_escape_string($db, $_POST['name']);
    $lastname  = mysqli_real_escape_string($db, $_POST['lastname']);
    $username  = mysqli_real_escape_string($db, $_POST['username']);
    $email     = mysqli_real_escape_string($db, $_POST['email']);
    $password  = mysqli_real_escape_string($db, $_POST['password']);
    $password2 = mysqli_real_escape_string($db, $_POST['password2']);

    if ($password == $password2) {
        $password = ($password);
        $sql      = "select * from account_info where (username='$username' or email='$email')";
        $res      = mysqli_query($db, $sql); // you were calling $res but it wasn't defined; this connects to the DB and executes SQL and then assigns the result
        if (mysqli_num_rows($res) > 0) {
            $row = mysqli_fetch_assoc($res);
            if ($username == $row['username']) {
                $_SESSION['message'] = "Username je vec registrovan";
            } elseif ($email == $row['email']) {  // changed `else` to `elseif` to include the condition, `else` doesn't accept conditional checks
                $_SESSION['message'] = "Email je vec registrovan";  // added ;
            } else {
                $sql = "INSERT INTO users(name, lastname, username, email, password) VALUES('$name' , '$lastname' , '$username' , '$email' , '$password')";
                mysqli_query($db, $sql);
                $_SESSION['message'] = "Sada si ulogovan";
                $_SESSION['message'] = $username;
                header("location:login.php");
            }
        } // required to close `if (mysqli_num_rows($res) > 0)`
    } // required to close the password checking condition
    else {
        $_SESSION['message'] = "Ne podudaraju se lozinke!";
    }
}
?>

但無法正常工作錯誤代碼：

警告：mysqli_num_rows（）期望參數1為mysqli_result，在第17行的Z：\\ Programs \\ XAMPP \\ htdocs \\ register.php中給出的布爾值