PHP登录 - mysql_fetch_array返回NULL

Question

我正在尝试设置一个简单的帐户登录设置和功能;但是，在运行我的“登录”时功能我似乎一直在打击＆＃39;不成功登录＆＃39;。

我使用var_dump函数尝试找到问题，并看到var_dump($row['username']); die;返回NULL。我觉得问题可能来自我的mysql_query或mysql_fetch_array。

非常感谢任何帮助。

<?php
    $host = 'localhost';
    $database = 'database_name';
    $username = 'username';
    $password = 'password';

    // Create connection
    $conn = mysql_connect($host, $username, $password);

    // Check connection
    if ($conn->connect_error) {
        die('Connection failed: ' . $conn->connect_error);
    }

    echo 'Connected successfully. ';

    mysql_select_db($database) or die('Unable to select database. ');

    $signIn = $_POST['signIn'];

    function signIn() {
        // Start session
        session_start();

        // Variables
        $ID = $_POST['username'];
        $Password = $_POST['password'];

        if (!empty($ID)) {
            $query = mysql_query('SELECT * FROM `signin` WHERE username = "$ID" AND password = "$Password"');
            $row = mysql_fetch_array($query, MYSQL_ASSOC);

            // Troubleshooting
            var_dump($row['username']); die;

            if (!empty($row['username']) AND !empty($row['password'])) {
                $_SESSION['username'] = $row['password'];

                echo "Successful login. ";
            } else {
                echo "Unsuccessful login. ";
            }
        }
    }

    if(isset($signIn)) {
        signIn();
    }
?>

下面是当前数据库表结构的屏幕截图。

Answer 1

问题是变量插值：

mysql_query('SELECT * FROM `signin` WHERE username = "$ID" AND password = "$Password"');

单引号不会将$ ID和$ Password扩展到查询中的值，您需要使用双引号：

mysql_query("SELECT * FROM `signin` WHERE username = '$ID' AND password = '$Password'");