MySQLi num_rows准备好的语句返回0行

Question

我使用include_once调用一个名为getTrysLeft的外部文件中的函数，该文件检查用户在最近的2小时内尝试登录的次数。问题是它总是返回0.如果我通过PHPMyAdmin运行SQL它返回行但我的代码总是返回0.导致它显示错误行数的错误是什么？以下是相关代码：

<?php
include_once 'db_connect.php'; 
include_once 'functions.php';

...

elseif ($loginstatus == 2)
{
    $now = time();
    $valid_attempts = $now - (2 * 60 * 60);
    $numberofrows = getTrysLeft($user_id, $valid_attempts, $mysqli); /// Calling function located in functions.php
    $error = '<p class="error">The email address and the password does not match, try again. There are currently: '.$numberofrows.' attemts.</p>'; /// Error value, here I always see "0 attempts"              
    $_SESSION['lgnerror']= $error;
    header('Location: ../login.php');
    exit();
}

以下是getTrysLeft函数：

function getTrysLeft($user_id, $valid_attempts, $mysqli)
{
    if ($stmt = $mysqli->prepare("SELECT time FROM login_attempts WHERE user_id = ? AND time > ?")) 
    {
        $stmt->bind_param('ii', $user_id, $valid_attempts);
        $stmt->execute();
        $stmt->store_result();
        $numrows = $stmt->num_rows;
        $stmt->close();
        return $numrows;
    } 
    else 
    {
       /// Some error handling here, nothing relevant really    
    }   
}

那么你说错误是什么？为什么num_rows返回0，即使完全相同的SQL语句返回PHPMyAdmin中的行？