PHP 表单验证器/MySQL 插入

Question

我编写了一个小的 PHP 文件来获取发布到它的信息，然后检查以确保它不为空。如果它不为空，它会检查以确保用户名不存在。如果是，它会重定向。如果没有，它会将信息添加到 MySQL 数据库中。我不知道问题是什么，但是在按下表单上的提交按钮后尝试导航到它时，浏览器会显示一个错误，指出无法显示该页面。这是代码。

<?php
$firstname = $_POST['fname'];
$lastname = $_POST['lname'];
$email = $_POST['email'];
$username = $_POST['user'];
$password = $_POST['pass'];


$con = mysql_connect("localhost","USER","PASS");
if (!$con)
  {
  die('Could not connect: ' . mysql_error());
  }

mysql_select_db("zach_blogin", $con);

$query="SELECT username FROM members WHERE username=$username";



if (mysql_num_rows($username) > 0 ) {
  header("Location: register.php?invalid");
} else {
  $sql=("INSERT INTO members (username, password, FirstName, LastName, Email)
  VALUES ($username, $password, $firstname, $lastname, $email)");
  if (!mysql_query($sql,$con))
    {
    die('Error: ' . mysql_error());
    }
else {
  header("Location: register.php?required");
}
?>

Answer 1

您没有执行查询：

$query="SELECT username FROM members WHERE username=$username";
//You need to execute the query here before you get num of rows.
if (mysql_num_rows($username) > 0 ) // also mysql_num_query takes an object.

类似：

$query="SELECT username FROM members WHERE username=$username";
if(($result = mysql_query($query)) !== false) {
  if (mysql_num_rows($result) > 0 ) {
   .....
  }
}

Answer 2

改变这个

if (mysql_num_rows($username) > 0 ) {

到

if (mysql_num_rows(mysql_query($query)) > 0 ) {