警告：mysqli_num_rows() 期望参数 1 为 mysqli_result，bool 给定...我该怎么办？ [复制]

Question

这里是代码

if (isset($_POST['signUp']))
{
    $username = mysqli_real_escape_string($database_connect, trim($_POST['username']));
    $email = mysqli_real_escape_string($database_connect, trim($_POST['email']));
    $password = mysqli_real_escape_string($database_connect, trim($_POST['password']));
    $password2 = mysqli_real_escape_string($database_connect, trim($_POST['password2']));

    if (!empty($username) && !empty($email) && !empty($password) && !empty($password2)
                 && $password == $password2)
        $query = "SELECT * from 'users' WHERE username = '$username'";
        $data = mysqli_query($database_connect, $query);
        if (mysqli_num_rows($data) == 0) {
            $query = "INSERT INTO 'users' (username, email, password, password2) VALUES('$username', '$email', SHA('$password'), SHA('$password2'))";
            mysqli_query($database_connect, $query);
            echo "OK";
            mysqli_close($database_connect);
            exit();
        } else {
            echo "Such login already exists";
        }

我该怎么办？ P.S 我已经在 Stack Overflow 上搜索过这个问题，但没有找到解决方案。

Answer 1

您应该阅读 mysqli::query 的文档。它返回一个mixed 类型——当你的查询失败时，它返回false，不是一个有效的结果。所以..您的查询一定失败了。

在使用$data之前，你需要检查是否$data === false。