检查数据库中是否已存在用户名和电子邮件[重复]

Question

我刚开始使用 php，如果您键入已经存在的用户名或密码，我尝试创建系统以拒绝“创建帐户”。谢谢，抱歉我的英语不好。 我已经尝试过了。不工作：link

这是我的 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

您在此行之前错过了非常重要的一行 if (mysqli_num_rows($res) > 0)

$sql="select * from account_info where username='$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()被调用了2次。
去掉if ($password == $password2) {里面的重复调用
您的代码还缺少 ; 和一些 }（用于正确关闭您的 if 条件）

现在的解决方案：
在处理数据库查询的结果之前，您需要连接到数据库并执行适当的 SQL 命令，然后您才会得到您想要的结果。您的代码缺少此过程。
在下面的代码中检查我的 cmets↓，然后在更正的代码中再次检查

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
          }

更正的代码：

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!";
    }
}

建议：

1. 使用准备好的语句而不是直接将用户提供的输入传递到 SQL
   （关键，您当前的代码容易受到 SQL 注入的攻击）
2. 使用支持 PHP 并提供语法高亮的 IDE（Atom、Visual Studio Code、PhpStorm 等）

Answer 3

我试过了

<?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!";
    }
}
?>

但不工作错误代码：

警告：mysqli_num_rows() 期望参数 1 为 mysqli_result， 第 17 行 Z:\Programs\XAMPP\htdocs\register.php 中给出的布尔值