如何在此PHP中添加注册验证？

Question

如何添加注册验证，以便用户无法使用与其他用户相同的用户ID？我被困在这里，因为我已经尝试了所有代码而没有任何工作。它会崩溃我的应用程序。

我正在使用Eclipse来完成我的应用。

我的php文件

<?php

/*
 * Following code will create a new product row
 * All product details are read from HTTP Post Request

 */

// array for JSON response
$response = array();

// check for required fields
if (isset($_POST['user_name']) && isset($_POST['user_pwd'])){

    $user_name = $_POST['user_name'];
    $user_pwd = $_POST['user_pwd'];


    // include db connect class
    require_once __DIR__ . '/db_connect.php';

    // connecting to db
    $db = new DB_CONNECT();

    // mysql inserting a new row
    $result = mysql_query("INSERT INTO doc_user (user_name, user_pwd) VALUES('$user_name', '$user_pwd')");


     // check if row inserted or not
    if ($result) {
        // successfully inserted into database
        $response["success"] = 1;
        $response["message"] = "Product successfully created.";

        // echoing JSON response
        echo json_encode($response);
    } else {
        // failed to insert row
        $response["success"] = 0;
        $response["message"] = "Oops! An error occurred.";

        // echoing JSON response
        echo json_encode($response);
    }
} else {
    // required field is missing
    $response["success"] = 0;
    $response["message"] = "Required field(s) is missing";

    // echoing JSON response
    echo json_encode($response);


}

Answer 1

在代码中更改此部分

// connecting to db
$db = new DB_CONNECT();

// chack database
$result = mysql_query("select user_name from doc_user where user_name = '$user_name'");
if(mysql_num_rows($result)){
    $response["success"] = 0;
    $response["message"] = "username not available.";

    // echoing JSON response
    echo json_encode($response);
    exit;
}

// mysql inserting a new row
$result = mysql_query("INSERT INTO doc_user (user_name, user_pwd) VALUES('$user_name', '$user_pwd')");