无法检查用户名是否存在 [英] unable to check username exists or not

问题描述

我创建了一个注册程序，将用户名密码插入到 mysql 数据库中.我现在正在尝试检查用户名是否存在.我编写了以下程序.它不工作.它显示mysql_num_rows() 期望参数 1 是资源."我真的需要你的专家建议

I have created a registration program which insert username password into mysql database. I am now trying to check the username exixts or not. I wrote the following program. its not working. it showing "mysql_num_rows() expects parameter 1 to be resource." I really need your expert suggestion

registration.php

<?php 
require 'jcon.php';
if(isset($_POST["username"], $_POST["firstname"],$_POST["password"])){
    $username=$_POST["username"];
    $firstname=$_POST["firstname"];
    $password=$_POST["password"];
}
$query = mysql_query("SELECT * FROM member WHERE username='$username'");
if(mysql_num_rows($query) != 0)
{
echo "Username already exists";
}
else{
$sql="INSERT INTO member (username, firstname, password)
VALUES ('$username', '$firstname','$password')";}
if(!mysqli_query($con,$sql)){
    die('Error: ' . mysqli_error($con));
}
echo "Dear {$firstname} ! you have been successfully registered. "
?>

推荐答案

它显示mysql_num_rows() 期望参数 1 是资源

it showing "mysql_num_rows() expects parameter 1 to be resource

这是mysql_query在失败时返回false从而触发臭名昭著的典型情况:

This is the typical case where mysql_query returns false upon failure therefore triggering the infamous:

mysql_num_rows() 期望参数 1 为资源

mysql_num_rows() expects parameter 1 to be resource

这可能是由多种因素造成的.尝试在 phpMyAdmin 或直接到数据库中运行查询并查看错误或通过 mysql_error.

This can be caused by multiple factors. Try running the query in phpMyAdmin or directly to the database and see the error or fetch the last mysql error via mysql_error.

最好始终检查 mysql_query 的返回值是否为 false 或 mysql_error 字符串是否为空:

It's good practice to always check if the returned value of mysql_query is false or if the mysql_error string is not empty:

if ($result and empty(mysql_error()))
    // everything ok

注意:永远不要混合使用 mysql_ 和 mysqli_ 函数.如果您必须选择我会选择 mysqli，因为 mysql_* 函数被认为已弃用.

Note: Never ever mix mysql_ and mysqli_ functions. If you have to choose I'd go with mysqli since mysql_* functions are considered deprecated.

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